Hydrothermal synthesis of mesoporous materials from diatomaceous earth has been carried out under saturated steam pressure (0.2-1.56 MPa) at 393-473 K for up to 72 h by slaked lime introduction. During the hydrothermal synthesis process, calcium silicate hydrate (CSH) was among the first phase formed and invariably appeared before tobermorite. The CSH formation seemed to exert a positive effect on the strength development and pore size evolution initially; whilst the tobermorite formation appeared to further enhance the strength and narrow the pore size. With curing at 473 K for 18 h, both of the strength and pore size distribution tended to reach optimal at which the pore size distribution also ranges between mesoporous area (2-50 nm in diameter). The highest strength seemed to coincide with the finest pore size distribution of the synthesized porous material during hydrothermal processing in this study. (c) 2007 American Institute of Chemical Engineers.