The objective of this investigation is to study the variation of strength of dual phase steel with the percentage of carbon content in the martensite phase. The study is conducted on samples of dual phase steel prepared by intercritical annealing process with temperature varying from 730oC to 810oC. In this process both coarse and fine ferrite- martensite structures are produced with volume fraction of martensite varying from 48 to 69%. It has been observed from the investigation that both yield strength and tensile strength increased with increasing carbon content in the martensite phase of dual phase steel up to 0.195% and then decreased. The optimum values of strength are observed at 0.195 % of carbon