Fe (x) Pt100-x (70.1 a parts per thousand currency sign x a parts per thousand currency sign 83.4) thin films with ordered Fe3Pt phase were grown successfully onto MgO(110) substrates by electron beam evaporation. The unit cell of ordered Fe3Pt phase is elongated along c-axis direction and the thin films become more chemically ordered with decreasing Fe content. The magnetization of thin films shows a decrease when Fe content is around 79 at.%. The relationship between magnetic anisotropy and structural parameters suggests that the change of magnetic anisotropy in ordered Fe3Pt thin films with different compositions most likely stems from the magnetocrystalline origin.