The magnetic properties and microstructural evolution of Zr-doped FePt alloy films prepared by dc-magnetron sputtering were investigated. Compared to an undoped Fe59Pt41 binary film, Zr-doped FePt alloy films showed accelerated ordering transformation kinetics accompanying smaller grains: we were able to fabricate a Zr-doped FePt film [e.g., (Fe59Pt41)97Zr3] possessing very fine grain size (5 nm in average) and high coercivity (7.3 kOe) within 10 min annealing at 500 °C. It is thought that the point defects and lattice strain introduced by Zr-doping activated the nucleation rate of the ordered phase. In particular, for Zr-doped FePt films containing less than 45 at. % Pt, the ordered L10 phase was decomposed into a disordered phase after excessive annealing due to the formation of a Pt–Zr compound, most likely Pt3Zr, that reduces the effective Pt content in the ordered phase. © 2001 American Institute of Physics.