diff --git a/zetaclient/chains/evm/base/logger.go b/zetaclient/chains/evm/base/logger.go
new file mode 100644
index 0000000000..c675450d2d
--- /dev/null
+++ b/zetaclient/chains/evm/base/logger.go
@@ -0,0 +1,21 @@
+package base
+
+import "github.com/rs/zerolog"
+
+// ObserverLogger is the base logger for chain observers
+type ObserverLogger struct {
+	// the parent logger for the chain observer
+	Chain zerolog.Logger
+
+	// the logger for inbound transactions
+	Inbound zerolog.Logger
+
+	// the logger for outbound transactions
+	Outbound zerolog.Logger
+
+	// the logger for the chain's gas price
+	GasPrice zerolog.Logger
+
+	// the logger for the compliance check
+	Compliance zerolog.Logger
+}
diff --git a/zetaclient/chains/evm/base/observer.go b/zetaclient/chains/evm/base/observer.go
new file mode 100644
index 0000000000..29fc185256
--- /dev/null
+++ b/zetaclient/chains/evm/base/observer.go
@@ -0,0 +1,252 @@
+package base
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"sync/atomic"
+
+	lru "github.com/hashicorp/golang-lru"
+	"github.com/pkg/errors"
+	"github.com/rs/zerolog"
+	"github.com/zeta-chain/zetacore/pkg/chains"
+	"github.com/zeta-chain/zetacore/zetaclient/context"
+	"github.com/zeta-chain/zetacore/zetaclient/metrics"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+
+	observertypes "github.com/zeta-chain/zetacore/x/observer/types"
+	"github.com/zeta-chain/zetacore/zetaclient/chains/interfaces"
+	clienttypes "github.com/zeta-chain/zetacore/zetaclient/types"
+)
+
+// Observer is the base chain observer
+type Observer struct {
+	// the external chain
+	chain chains.Chain
+
+	// the external chain parameters
+	chainParams observertypes.ChainParams
+
+	// zetacore context
+	zetacoreContext *context.ZetacoreContext
+
+	// zetacore client
+	zetacoreClient interfaces.ZetacoreClient
+
+	// tss signer
+	tss interfaces.TSSSigner
+
+	// the latest block height of external chain
+	lastBlock uint64
+
+	// the last successfully scanned block height
+	lastBlockScanned uint64
+
+	// lru cache for chain blocks
+	blockCache *lru.Cache
+
+	// observer database for persistency
+	db *gorm.DB
+
+	// the channel to stop the observer
+	stop chan struct{}
+
+	// telemetry server
+	ts *metrics.TelemetryServer
+}
+
+// NewObserver creates a new base observer
+func NewObserver(
+	chain chains.Chain,
+	chainParams observertypes.ChainParams,
+	zetacoreContext *context.ZetacoreContext,
+	zetacoreClient interfaces.ZetacoreClient,
+	tss interfaces.TSSSigner,
+	dbPath string,
+	ts *metrics.TelemetryServer,
+) (*Observer, error) {
+	ob := Observer{
+		chain:            chain,
+		chainParams:      chainParams,
+		zetacoreContext:  zetacoreContext,
+		zetacoreClient:   zetacoreClient,
+		tss:              tss,
+		lastBlock:        0,
+		lastBlockScanned: 0,
+		stop:             make(chan struct{}),
+		ts:               ts,
+	}
+
+	// create block cache
+	var err error
+	ob.blockCache, err = lru.New(1000)
+	if err != nil {
+		return nil, err
+	}
+
+	// open database
+	err = ob.OpenDB(dbPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return &ob, nil
+}
+
+// Chain returns the chain for the observer
+func (ob *Observer) Chain() chains.Chain {
+	return ob.chain
+}
+
+// WithChain attaches a new chain to the observer
+func (ob *Observer) WithChain(chain chains.Chain) *Observer {
+	ob.chain = chain
+	return ob
+}
+
+// ChainParams returns the chain params for the observer
+func (ob *Observer) ChainParams() observertypes.ChainParams {
+	return ob.chainParams
+}
+
+// WithChainParams attaches a new chain params to the observer
+func (ob *Observer) WithChainParams(params observertypes.ChainParams) *Observer {
+	ob.chainParams = params
+	return ob
+}
+
+// ZetacoreContext returns the zetacore context for the observer
+func (ob *Observer) ZetacoreContext() *context.ZetacoreContext {
+	return ob.zetacoreContext
+}
+
+// WithZetacoreClient attaches a new zetacore client to the observer
+func (ob *Observer) WithZetacoreClient(client interfaces.ZetacoreClient) *Observer {
+	ob.zetacoreClient = client
+	return ob
+}
+
+// GetLastBlock get external last block height
+func (ob *Observer) GetLastBlock() uint64 {
+	return atomic.LoadUint64(&ob.lastBlock)
+}
+
+// SetLastBlock set external last block height
+func (ob *Observer) SetLastBlock(height uint64) {
+	atomic.StoreUint64(&ob.lastBlock, height)
+}
+
+// GetLastBlockScanned get last block scanned (not necessarily caught up with external block; could be slow/paused)
+func (ob *Observer) GetLastBlockScanned() uint64 {
+	height := atomic.LoadUint64(&ob.lastBlockScanned)
+	return height
+}
+
+// SetLastBlockScanned set last block scanned (not necessarily caught up with external block; could be slow/paused)
+func (ob *Observer) SetLastBlockScanned(blockNumber uint64) {
+	atomic.StoreUint64(&ob.lastBlockScanned, blockNumber)
+	metrics.LastScannedBlockNumber.WithLabelValues(ob.chain.ChainName.String()).Set(float64(blockNumber))
+}
+
+// BlockCache returns the block cache for the observer
+func (ob *Observer) BlockCache() *lru.Cache {
+	return ob.blockCache
+}
+
+// WithBlockCache attaches a new block cache to the observer
+func (ob *Observer) WithBlockCache(cache *lru.Cache) *Observer {
+	ob.blockCache = cache
+	return ob
+}
+
+// Stop returns the stop channel for the observer
+func (ob *Observer) Stop() chan struct{} {
+	return ob.stop
+}
+
+// TelemetryServer returns the telemetry server for the observer
+func (ob *Observer) TelemetryServer() *metrics.TelemetryServer {
+	return ob.ts
+}
+
+// OpenDB open sql database in the given path
+func (ob *Observer) OpenDB(dbPath string) error {
+	if dbPath != "" {
+		// create db path if not exist
+		if _, err := os.Stat(dbPath); os.IsNotExist(err) {
+			err := os.MkdirAll(dbPath, os.ModePerm)
+			if err != nil {
+				return errors.Wrap(err, "error creating db path")
+			}
+		}
+
+		// open db by chain name
+		chainName := ob.chain.ChainName.String()
+		path := fmt.Sprintf("%s/%s", dbPath, chainName)
+		db, err := gorm.Open(sqlite.Open(path), &gorm.Config{})
+		if err != nil {
+			return errors.Wrap(err, fmt.Sprintf("error opening observer db for chain: %s", chainName))
+		}
+
+		// migrate db
+		err = db.AutoMigrate(&clienttypes.ReceiptSQLType{},
+			&clienttypes.TransactionSQLType{},
+			&clienttypes.LastBlockSQLType{})
+		if err != nil {
+			return errors.Wrap(err, fmt.Sprintf("error migrating observer db for chain: %s", chainName))
+		}
+		ob.db = db
+	}
+	return nil
+}
+
+// LoadLastBlockScanned loads last scanned block from environment variable or from database
+// The last scanned block is the height from which the observer should start scanning for inbound transactions
+func (ob *Observer) LoadLastBlockScanned(logger zerolog.Logger) (fromLatest bool, err error) {
+	// get environment variable
+	envvar := ob.chain.ChainName.String() + "_SCAN_FROM"
+	scanFromBlock := os.Getenv(envvar)
+
+	// load from environment variable if set
+	if scanFromBlock != "" {
+		logger.Info().
+			Msgf("LoadLastBlockScanned: envvar %s is set; scan from  block %s", envvar, scanFromBlock)
+		if scanFromBlock == clienttypes.EnvVarLatest {
+			return true, nil
+		}
+		blockNumber, err := strconv.ParseUint(scanFromBlock, 10, 64)
+		if err != nil {
+			return false, err
+		}
+		ob.SetLastBlockScanned(blockNumber)
+		return false, nil
+	}
+
+	// load from DB otherwise. If not found, start from latest block
+	blockNumber, err := ob.ReadLastBlockScannedFromDB()
+	if err != nil {
+		logger.Info().Msgf("LoadLastBlockScanned: chain %d starts scanning from latest block", ob.chain.ChainId)
+		return true, nil
+	}
+	ob.SetLastBlockScanned(blockNumber)
+	logger.Info().
+		Msgf("LoadLastBlockScanned: chain %d starts scanning from block %d", ob.chain.ChainId, ob.GetLastBlockScanned())
+
+	return false, nil
+}
+
+// WriteLastBlockScannedToDB saves the last scanned block to the database
+func (ob *Observer) WriteLastBlockScannedToDB(lastScannedBlock uint64) error {
+	return ob.db.Save(clienttypes.ToLastBlockSQLType(lastScannedBlock)).Error
+}
+
+// ReadLastBlockScannedFromDB reads the last scanned block from the database
+func (ob *Observer) ReadLastBlockScannedFromDB() (uint64, error) {
+	var lastBlock clienttypes.LastBlockSQLType
+	if err := ob.db.First(&lastBlock, clienttypes.LastBlockNumID).Error; err != nil {
+		// not found
+		return 0, err
+	}
+	return lastBlock.Num, nil
+}
diff --git a/zetaclient/chains/evm/base/observer_test.go b/zetaclient/chains/evm/base/observer_test.go
new file mode 100644
index 0000000000..49e0890e7c
--- /dev/null
+++ b/zetaclient/chains/evm/base/observer_test.go
@@ -0,0 +1,11 @@
+package base_test
+
+import (
+	"testing"
+)
+
+func TestNewObserver(t *testing.T) {
+}
+
+func TestChain(t *testing.T) {
+}
diff --git a/zetaclient/chains/evm/base/signer.go b/zetaclient/chains/evm/base/signer.go
new file mode 100644
index 0000000000..22f1111448
--- /dev/null
+++ b/zetaclient/chains/evm/base/signer.go
@@ -0,0 +1 @@
+package base