The γ-Fe2O3 surface evapourated with Co has been studied by photoemission spectros-copy. The results show that at low coverage, Co is very active and combined with the oxygen in γ-Fe2O3, while Fe in γ-Fe2O3 was reduced; at the coverage of 0.2-0.8 monolayer, some kind of CoFe2O4-like oxide was formed on the surface; with further Co coverage increasing, the Fe in the bulk began to segregate to the surface and the second monolayer of Co began to form on the surface, which destroyed the condition favourable to the formation of the oxide. We can conclude from these results that the magnetism improvement of magnetic powder coated with one- or sub- monolayer Co may have strong relation to the presence of this CoFe2O4-like oxide.