Thin films of Pt-Mn-Sb alloy prepared by RF sputtering were deposited onto glass and silica substrates at room temperature and at 573K under argon pressures of 1.33∼26.6Pa, and the targets were altered by changing the number of Pt and Mn chips on Pt-Mn-Sb alloys. The composition and structure of the deposited films were determined by EPMA and X-ray diffraction. In order to prepare PtMnSb Heusler alloy, the target composition should be about 21Pt-53Mn-26Sb. The compositional range making the PtMnSb phase was in the vicinity of the stoichiometric composition. Films prepared at low argon pressures and low substrate temperatures were nearly amorphous, but they crystallized when heated above 573K.