In this report, the γ-Fe2O3 fine particles with Co-doping was investigated by means of M?ssbauer effect of 57Fe.The experimental result indicates that the effective anisotropy constant of the γ-Fe2O3 fine particles doped with Co is about 30% greater than that of the superfine γ-Fe2O3 powder without Co. It provides a further explanation to the increasing of the coercivity of the ordinary needle γ-Fe2O3 powder with Co-doping.