On the calcium silicate hydrothermal reaction, the effect of NaOH and KOH Studied. Forincreasing the yield of fibers and to promote crystal growth, Rotary autoclae has been used. By addition NaOH solution, approximately 150${mu}{ extrm}{m}$ of pectolite was grown. By addition KOH solution, approximately 30${mu}{ extrm}{m}$ of 11$AA$-Tobermorite was grown under the conditon of 21$0^{circ}C$ 10 days reaction. These results indicate that 11$AA$-Tobermorite was stabilized by KOH over a wide Temperature and composition range.