Thermal expansion property of $SiO_2-Al_2O_3$ system consisted of Muan clay, Hadong Pink Kaolin and Dangjin Silica was studied. Specimens were heated at the constant rate of 18$0^{circ}C$/hr to the max. temperatures of 115$0^{circ}C$ to 130$0^{circ}C$ with an interval of $25^{circ}C$, and matured for 3hrs. The result of X-Ray diffraction analysis showed that main crystals formed were $alpha$-quartz, $alpha$-cristobalite and mullite. Linear thermal expansion was measured at 90$0^{circ}C$. The results of the linear thermal expansion were decreased regularly with the increase of the sintering temperature in accordance with the following equation. $y=5$chi$perp1100^{circ}$</TEX>. Where $chi$ is amounts of kaolin (wt%), and y is temperature of the changing point of linear thermal expansion.