diff --git a/backend/mpc-system/migrations/005_add_delegate_party_id.down.sql b/backend/mpc-system/migrations/005_add_delegate_party_id.down.sql
new file mode 100644
index 00000000..b7a5180a
--- /dev/null
+++ b/backend/mpc-system/migrations/005_add_delegate_party_id.down.sql
@@ -0,0 +1,3 @@
+-- Remove delegate_party_id column from mpc_sessions table
+DROP INDEX IF EXISTS idx_mpc_sessions_delegate_party;
+ALTER TABLE mpc_sessions DROP COLUMN IF EXISTS delegate_party_id;
diff --git a/backend/mpc-system/migrations/005_add_delegate_party_id.up.sql b/backend/mpc-system/migrations/005_add_delegate_party_id.up.sql
new file mode 100644
index 00000000..6d793310
--- /dev/null
+++ b/backend/mpc-system/migrations/005_add_delegate_party_id.up.sql
@@ -0,0 +1,10 @@
+-- Add delegate_party_id column to mpc_sessions table
+-- This column stores the ID of the delegate party that will return user's share
+-- Only populated for keygen sessions with require_delegate=true
+ALTER TABLE mpc_sessions ADD COLUMN delegate_party_id VARCHAR(255) DEFAULT '';
+
+-- Add index for faster lookups by delegate party
+CREATE INDEX idx_mpc_sessions_delegate_party ON mpc_sessions(delegate_party_id) WHERE delegate_party_id != '';
+
+-- Add comment
+COMMENT ON COLUMN mpc_sessions.delegate_party_id IS 'The delegate party ID that generates and returns user share (for keygen sessions with delegate)';