Fullerenes (C60 and C70) films have been fabricated by a thermal evaporation method. Raman spectra for C60 and C70 films were utilized to evaluate the film quality, and atomic force microscopy technique showed the roughness of both films was within the molecular scale of fullerenes. Moreover, these fullerenes (C60 and C70) films were successfully used to fabricate spin-valve devices with an Fe3O4/AlO/fullerenes (C60 or C70)/Co/Al stacking structure to get an insight for spin conserved electron transport behaviors in C60 and C70 films. The magnetoresistance (MR) effects in these devices were investigated at both room and low temperatures. As reducing measurement temperature, the MR ratios increased in both fullerenes (C60 and C70) based devices due to the reduction of spin scattering. It is worth noting that the MR ratio in C60 based devices is around one order of magnitude larger than that of C70 based devices at room temperature. The dominant reason for the larger MR ratio in C60 based spin valves compared to that in C70 based devices is analyzed. This study may provide some criteria for organic semiconductors selection for designing spin based organic devices.