We have investigated growth morphology of FePt/Pt films prepared by sputtering on a MgO (100) substrate in a temperature range of 100–600 °C. The L10 ordered structure appeared at a low substrate temperature of 200 °C and became a dominant phase via a second-order type transformation. A transition of FePt film growth morphology from continuous two-dimensional (2D) layer-by-layer mode into 3D island growth mode was observed at a substrate temperature of about 400 °C. When the film grew in continuous mode the stress from lattice misfit played an important role in governing the growth morphology; while growing in island mode the thermal stress increasingly influenced it. The island structure revealed eightfold symmetry following the preferred process of elongating the channel length to broadening its width. © 2001 American Institute of Physics.