Additives for low temperature sintering of mullite ceramics were investigated for matching Mo-Cu conducting paste with that ceramics at 1,400$^{circ}C$. $SiO_2$, MgO and $Y_2O_3$ were chosen as the additives for low temperature sintering, and the amounts of those additives were varied with sintering temperature of 1,400$^{circ}C$ to 1,500$^{circ}C$. With additives of 1.0 wt% of $SiO_2$, 1.0 wt% of MgO, and 1.5 wt% of $Y_2O_3$, the densest sintered body of 3.12 g/$cm^3$ was obtained at 1,400$^{circ}C$ in reducing atmosphere. The flexural strength of that was 325 MPa and the CTE (Coefficient of thermal expansion) was 4.33 ppm/$^{circ}C$.