A large positive magnetoresistance (MR) has been observed in Cox-C1-x gr anular films prepared on Si(100) substrates by pulsed laser deposition (PLD). Co 0.02-C0.98 sample has the largest room-temperature MR of 2 2% at the magnetic field B=1T. It is noted that in the Cox-C1-x/Si s tructure, the MR at room-temperature is much larger than that at low temperatures. The room-te mperature positive MR of the Cox-C1-x films has a B2/ 3 dependence when B＜1T and a B1/2 dependence when B＞1T. Such magnetotransport pr opert ies have never been reported before. It appears that some new mechanisms play im portant roles in the magnetotransport of the Cox-C1-x film s. Further stu dy on the MR mechanism of the Cox-C1-x/Si structure will n ot only shed l ight on the study of spin electronics and magnetism, but also make possible the application of the Cox-C1-x/Si in information industry.