Micro/mesoporous SiOC bulk ceramics with the highest surface area and the narrowest pore size distribution were prepared by water-assisted pyrolysis of polysiloxane in argon atmosphere at controlled temperatures (1100 degrees C-1400 degrees C) followed by etching in hydrofluoric acid (HF) solution. Their pyrolysis behaviors, phase compositions, and microstructures were investigated by DSC, FTIR, XRD, and BET. The Si-O-Si bonds, SiO2-rich clusters, and SiO2 nanocrystals in the pyrolyzed products act as pore-forming species and could be etched away by HF. Water injection time and pyrolysis temperature have important effects on phase compositions and microstructures of the porous SiOC bulk ceramics, which have a maximum-specific surface area of 2391.60m(2)/g and an average pore size of 2.87nm. The porous SiOC ceramics consist of free carbon phase, silicon carbide, and silicon oxycarbide.