In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200 °C for 2 h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100 °C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150 °C. Further growth in austenite grains at 1200 °C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100 °C for 2 h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties.