This study investigates how heat treatment affects both the mechanical behavior and the morphology of martensite in high-strength martensite-ferrite dual-phase (DP) steel. A DP800 steel underwent heat treatment to induce various forms of martensite morphology. Analyses of mechanical behavior of the DP steel samples before and after heat treatment have demonstrated that the heat treatment improves hardness and mechanical proprieties. To study the influence of heat treatment on dual-phase steels, analyzes of the mechanical behavior of these DP steel samples were carried out before and after this treatment. The results have shown that improvements in hardness and mechanical properties were achieved through heat treatment. Among different treatments, inter-critical treatment has resulted in achieving the optimal combination of ductility, strength and stiffness. The results indicated a significant increase in ultimate tensile strength and microhardness. They were remarkably increased by 53% and 71% respectively. The observed tensile ductility has been linked to the influence of martensite morphology.