The FePt(30 nm)/MgO bilayer films with various MgO(200) underlayer thicknesses of 0 to 30 nm are in-situ deposited on Si substrates. A weak (111)FePt peak as well as strong (001)FePt and (002)FePt peaks are observed in XRD pattern of single-layered FePt film with no MgO underlayer. When a 5 nm thick MgO film is introduced under the FePt film, the (111)FePt peak almost disappears and both the (001)FePt and (002)FePt peaks are enhanced greatly. This indicates that the perpendicular magnetic anisotropy of FePt film can be improved by introduction of a thinner MgO underlayer. However, a weak (111)FePt peak appears again as the MgO underlayer is increased to 10 nm, revealing that the perpendicular magnetic anisotropy of FePt film will be deteriorated by introducing a thicker MgO underlayer.