A method for fabricating metal gate transistor is disclosed. The method includes the steps of: providing a substrate having a NMOS region and a PMOS region; forming a dummy gate on each of the NMOS region and the PMOS region respectively; removing the dummy gates from each of the NMOS region and the PMOS region; forming a n-type work function layer on the NMOS region and the PMOS region; removing the n-type work function layer in the PMOS region; forming a p-type work function layer on the NMOS region and the PMOS region; and depositing a low resistance metal layer on the p-type work function layer of the NMOS region and the PMOS region.