The porous wollastonite ceramics were fabricated after firing calcium silicates, obtained using natural resources and by-products of power plants by hydrothermal synthesis, without organic fibers or asbestos for reinforcement agent. A specimen from diatomite as a SiO2 staring raw material had the highest strength owing to normal grain growth and good densification from homogeneous sperhcial C-S-H hydrates. A specimen from SiO2 sol as a SiO2 starting raw material showed tobermolite, but fly ash and mixed system did xonotlite after hydrothermal synthesis. The specimen from fly ash showed the lowest firing shirikage and strength changes in the firing range from 50$0^{circ}C$ to 120$0^{circ}C$. The other phases in all specimens changed to wollastonite phase after firing at 100$0^{circ}C$. Also the average pore size was distributed from 0.2${mu}{ extrm}{m}$ to 2${mu}{ extrm}{m}$.