Yttrium iron garnet films were grown by radio frequency magnetron sputtering on Si(111) substrate with and without CeO2 buffer layer, and influence of CeO2 buffer on the microstructure and magnetic behaviors of the films were investigated. As compared with the film without buffer, a larger saturation magnetizaton (Ms), lower coercive force (Hc), and higher remnant magnetization (Mr) were obtained due to the introduction of CeO2 layer. The higher Ms results from the denser structure and the smaller content of Fe2+ ions. The lower Hc and higher Mr can be explained by the small surface roughness and crystal grains size. The film on CeO2 buffer layer possess fine microstructure and its surface roughness is smaller than the unbuffered films, which provides an increased exchange between the crystal grains and an enhanced spontaneous magnetization effect, leading to the higher remnant magnetization.