i am using mysql as database. But MySqlTransaction is not working

Private objTrans As ODS.MySqlTransaction
cmdAcc.Connection = con
objTrans = con.BeginTransaction()
cmdAcc.Transaction = objTrans
Try
.........
...............
objTrans.Commit()
Catch Ex As Exception
.
.
objTrans.Rollback()
End Try

But this is not working.By default in mysql autocommit is true.
How we can change it in to false?