Ion-molecule reactions of silicon-carbon binary cluster ions SiCn+ (n=1-6) and SiCn- (n=2-4) with O-2 molecules were studied by using an rf ion trap. For all selected positive and negative parent ions, only SiCnO+ or SiCnO- were produced, respectively. The rate constants for the oxidation of these clusters were determined for the first time. The size dependence of the reactivities are discussed, and the presence of the ring form positive ions for n=3 and 5 are suggested.