Effects of the Os layer on the magnetic properties of FePt/Os/FePt were investigated. The magnetic layer of FePt in the as-deposited Ta/FePt/Os/FePt/Ta thin films exhibited very strong (1 1 1) orientation in all the cases. As the thickness of Os spacer layer between 1 and 3 Å, it appeared an antiferromagnetic exchange coupling (AFC) behavior. The exchange coupling transforms to ferromagnetic when the thickness of Os spacer layer was thicker than 4 Å. Although the J value for FePt/Os/FePt thin films is -0.22 erg/cm2, which is relatively small than that of Co/Ru system, the GMR effects could be observed. In general, the AFC in multilayer system shows the first maximum of AFC peak occurring at spacer thickness between 8 and 11 Å for most spacer materials. In our investigation, this is the first time that a clear AFC behavior observed in FePt/Os/FePt system with Os spacer thickness at 2 Å.