The study on magnetic properties of RF sputtered iron oxide thin films was carried out systematically. More specifically, the temperature dependence (77-500 K) of the coercivity and the variation of coercivity with different iron oxide phases such as the as-sputtered Fe3O4, partially transformed Fe3O4/(γ-Fe2O3), and γ-Fe2O3, were investigated. Comparing the theoretical analyses with the experimental results, the contributions to the coercivity from shape anisotropy, magnetocrystalline anisotropy, and stress-induced magnetic anisotropy were obtained separately. And the first-order crystalline anisotropy constant K1 vs. temperature for Fe3O4 and γ-Fe2O3 films was derived from Ms(T) and Hc(T) over the temperature range of 100-500 K.