Abstract: The effect of Ti-containing complex inclusions on the microstructure refinement of non-quenched and tempered steel was studied by using SEM and EDS. The room temperature tensile strength and absorbed-infracture energy of the tested steel were tested, and the fractography was observed. The results show that Ticontaining complex inclusions act as the nuclei for intra-granular ferrites and refine austenite grains, and with Ti added, the area proportion of ductile fracture is increased. The toughness of the studied steel is enhanced by about 50% while keeping the same strength level.