Abstract: The microstructure and mechanical properties of V-Ti,Nb-V-Ti microalloyed non-quenched and tempered steel were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy. The results show that the impact toughness can reach 50 J when rolling ratio is greater than or equal to 10 in the Nb-V-Ti microalloyed non-quenched and tempered steel. While the similar impact toughness is achieved when the rolling ratio reach and more than 15 in V-Ti non-quenched and tempered steel. According to the same rolling ratio, it can be found that impact toughness of Nb-V-Ti microalloyed steel is better than V-Ti non quenched and tempered steel. Niobium addition could raise the coarsening temperature of austenite, effectively inhibit quick growth of austenite, and reduce the grain size and space of pearlite lamellar. The rod cemenite gradually transformed into granular of spherical cemenite. Additionally, Nb could promote the precipitation of fine-dispersed carbides in V-Ti alloyed non-quenched and tempered steel. Therefore, after non-re-crystallization region deformation, tlie Nb-V-Ti alloyed steel could obtain the fine dual phase structure with ferrite and pearlite, and the relatively 900 °C temperature large deformation could further improve the strength and toughness of Nb-V- Ti non-quenched and tempered steel.