Abstract: Experiments were performed to investigate the effect of austenitizing temperature on the mechanical properties of quenched and tempered Ti-V microalloyed steel. Metallographic and transmission electron microscopy (TEM) observations reveal the variation of austenite grain size with austenitizing temperature. Within the temperature range of 850 to 1200℃, the austenite grain size experiences three phases, which are stable, rapidly increased, and stable again. Tensile strength and impact toughness tests show that, when the austenitizing temperature rises, the tensile strength R_m increases gradually, but the impact toughness undergoes a process of stabilizing, decreasing and then increasing. At a certain temperature, coarsening of precipitated particles leads to the sudden increase of austenite grain size. The increase of diffuse precipitates resulting from continuous solutionizing of microalloying elements with temperature rise and the effective pinning of precipitated particles are the main reasons for the increase of tensile strength, while abnormal grain growth and grain size uniformity at a certain temperature are the key factors that influence the toughness of the steel.