Mesoporous silicon carbide with and without SiC filler was prepared from the pyrolysis of polycarbosilane (PCS), and the relationship between pyrolysis and properties of micro/meso pores was investigated. The surface area of pyrolyzed PCS without filler significantly decreased from 268 to 0.5m2/g with increasing pyrolysis temperature, and disappearance of the micropores was observed. In contrast, the pyrolyzed PCS with filler showed the retention of micro/mesopores, regardless of pyrolysis temperature. In addition, high surface area ranging from 120 to 180m2/g and a bimodal pore distribution were observed in pyrolyzed PCS with filler. FT-IR showed the decomposition of Si-H, Si-CH3 and Si-CH2-Si in the PCS network during pyrolysis, which led to the evolution of hydrogen and methane gas. However, the obtained pores might be larger than the size of evolved gases. Thus, though micro/meso pores and large surface area were retained by the addition of filler, coalescence between pores could occur during pyrolysis.