The aim of this study was to investigate the effect of martensite morphology on tensile behavior of dual phase (DP) steel. For this propose, a cold-rolled low carbon steel (0.18wt.%C and 1.25wt.% Mn) was subjected to three different heat treatment cycles with the names of intercritical annealing (IA), step quenching (SQ) and intermediate quenching (IQ). IA cycle included an isothermal annealing in the intercritical region followed by water quenching, SQ included an austenitization step followed by intercritical annealing and water quenching, and IQ included an austenitization and water quenching to obtain a fully martensitic microstructure and subsequent intercritical annealing of this martensitic microstructure to obtain a DP microstructure. According to the results, the DP steel obtained by IQ which contained fine and fibrous martensite in the ferrite matrix had the highest ultimate tensile strength, uniform and total elongation and work hardening magnitude, while the step-quenched sample which contained large and blocky martensite in the ferrite matrix had the lowest value for the mentioned properties. All the samples showed a two-stage work hardening behavior based on the Hollomon analysis. The dominant fracture mechanism for all samples was ductile fracture mode.