Hydroxyapatites were prepared by the different $SiO_2$ addition at $1450^{circ}C$ for 2h. With the increase of $SiO_2$ addition, microstructure, bulk density, porosity, mechanical strength of $hydroxyapatite/{eta}-TCP$ composite were investigated. When the sintered HAp contained 1 wt% $SiO_2$, the each properties of the HAp were increased. But the excess addition of $SiO_2$ content above 1wt% the each property were decreased. This results were due to the ${eta}-TCP$ phase. The ${eta}-TCP$ phase appeared at 3 wt% $SiO_2$ addition and the ${eta}-TCP$ phase was enhanced by the $SiO_2$ increasing.