We have measured the spin-resolved photoemission spectra of the Co thin films grown epitaxially on Au(1 1 1) substrate in order to investigate their valence band structures. It is proved that the electronic structures of Co thin films are pretty different from that of bulk hcp-Co. It is observed that as the films grow thicker, the electronic structures become closer to those of the bulk Co with the magnetic anisotropy turning into in-plane magnetization from out-of-plane magnetization.