Surface oxidation occurred during pyrolysis of SiC particulate-reinforced composites (PRCs) with a precursor-derived Si-C-N matrix. In contrast, such an oxidation was not observed in pure Si-C-N ceramics. The present investigation discusses the possible reasons for this, and reports on the influence of such an oxidation on the microstructure and the mechanical and thermal properties of PRCs by the precursor-impregnation and pyrolysis method. The high-temperature mass stability of the PRCs in Ar deteriorated owing to the decomposition of SiO2 formed by oxidation. The effects of the pyrolysis schedule on the processing and mechanical properties of PRCs are also investigated.