Hierarchically porous silicon carbide (SiC) monoliths were fabricated based on polycarbosilane (PCS), divinyl benzene (DVB), and decalin, by a sequence of procedures including catalyst-free hydrosilylation reaction-induced phase separation, ambient-pressure drying, calcination, and HF etching. The influences of ratios of each component on the phase separation were systematically studied. It was found that isotactic polypropylene added as a nonreactive additive could effectively tailor the microstructure and improve the mechanical properties of SiC monoliths. The resultant SiC monoliths mainly consisted of -SiC nanocrystals, and possessed low bulk density (0.7g/cm(3)), high porosity (78%), large specific area (100.6m(2)/g), high compressive strength (13.5 +/- 1.6MPa), and hierarchical pores (macropores around 350nm, mesopores around 4 and 20nm). These properties make SiC monoliths promising materials for catalyst/catalyst support, gas separator, and the reinforcement of high-temperature composites.