The effect of oxygen partial pressure on Zn0.9Cr0.1O heteroepitaxial thin films grown by radio frequency sputtering has been investigated. The grown films on Si (100) substrates have been characterised by X-ray diffractometer (XRD), photoluminescence (PL), Hall effect measurements and vibrating sample magnetometer (VSM). The XRD pattern shows that the films are preferentially oriented along (002) diffraction plane. The Hall measurement shows that electron concentration of the films decreases with increase of oxygen partial pressure. The decrease in intensity of violet band emission and red shift in near-band-edge emission observed from room temperature PL measurement have been well consistent with our electrical measurements. The room temperature VSM measurements showed that the magnetic property of ZnO:Cr film have strong dependence on oxygen partial pressures and the film grown at low oxygen partial pressure exhibits better ferromagnetism.