Structure, magnetic and electrical transport properties of the polycrystalline (Fe3O4)(100-x)Pt-x composite films fabricated using DC reactive magnetron sputtering at ambient temperature were investigated systematically. It is found that the films are composed of inverse-spinel-structured polycrystalline Fe3O4 and Pt. Pt addition proves the growth of Fe3O4 grains with the (111) orientation. All the films are ferromagnetic at room temperature. The dominant magnetic reversal mechanism turns from domain wall motion to Stoner-Wohlfarth rotation with the increasing x. The electrical transport mechanism also changes with the increasing x because Pt addition decreases the height of the tunneling barrier at the Fe3O4 grain boundaries, and makes the magnetoresistance of the films decrease. (C) 2010 Elsevier B.V. All rights reserved.