Polycrystalline iron oxide films were fabricated using the reactive sputtering method without substrate heating. Structure characterization indicates that the dominant phases in the films evolve from α-Fe to pure Fe3O4 with the increasing O2 flow rate. In polycrystalline Fe3O4 films, disordered atoms exist at the grain boundaries. Magnetic properties analyses reveal that the room-temperature magnetization first decreases and later increases due to the variation of the volume fraction of the paramagnetic FeO phase with a Néel temperature of 198 K. The magnetoresistance MR (= [R(H) − R(0)]/R(0)) of the films increases from 0.1% for pure Fe film to 10.6% for the Fe3O4 film at 80 K under a 90 kOe field. The transport mechanism of FeO–Fe3O4 and Fe3O4 films is suggested to be the tunnelling process, which satisfies the log ρ ~ T−1/2 relation. The Hall resistivity of the Fe3O4 film decreases with increasing temperature. The ordinary and extraordinary Hall coefficients of the Fe3O4 film at 300 K are about 100 and 420 times larger than those of bulk Fe.