Effects of agitation and heating rate on crystallinity, size distribution and mean size of $alpha$-$SiO_2$powder prepared hydrothermally were investigated. $alpha$-$SiO_2$crystalline powder, in mean particle size of 1~3.2 $mu extrm{m}$, was obtained at $350^{circ}C$ using KOH as a mineralized for a 3 h reaction. Experimental results showed that particle size became smaller as the rate of agitation increased if it was introduced from the beginning of reaction, however, crystallinity was reduced at the low rate of agitation and it was became enhanced at above 150 r/min. Particle size became larger if agitation was introduced at any time during the reaction rather than introduced from the beginning of reaction. It was also found that particle size became smaller if heating rate was reduced, while the rate of agitation kept constant.