The effect of thermal strain on the quality factor of MgTiO3 at microwave frequencies was investigated as various cooling rates. The cooling rates were changed to 1C/min, 5C/min, 30C/min and air quenching. As the cooling rate increased, dielectric constant and temperature coefficient of resonant frequency of MgTiO3 ceramics did not change significantly. However the crystallographic strain calculated with full width at half miximum(FWHM) of MgTiO3 ceramics increased from 0.00565 to 0.0101 and the quality factor(Qf) decreased from 220,000 GHz to 150,000GHz as the cooling rate increased. This result can be explained by strain dependence on the deterioration of the quality factor.