In this work, different dual phase microstructures were produced in 15CrNiMo7 steel, in order to study the effect of martensite volume fraction, martensite morphology, and epitaxial ferrite on tensile strength and fatigue behavior. Mechanical properties of five different dual phase steels have been investigated by carrying out tensile, hardness and fatigue tests. By increasing the martensite content, both tensile and yield strengths increased. The presence of new ferrite caused a decrease in strength and an increase in ductility. It was observed that the fatigue strength increased with increasing martensite content and decreasing martensite size (fiber). The new ferrite caused a small amount of decrease in fatigue strength. Fractographic analysis after fatigue test was performed by using SEM. It was observed that the striation spacing decreased with increasing martensite content.