Currently dual phase steel are used in manufacture auto parts due to their good mechanical properties, which allow manufacture pieces more lightweight and therefore reduce the fuel consumption. However, the influence of their microstructure, which depends of a lot of factors like the chemical composition, on properties like fracture toughness or the crack propagation resistance haven´t had a large develop. Thus is convenient continue studying these properties, which allow estimate the final limit of use of a piece through structural integrity analysis. This document presents the study of influence of the dual phase steel microstructure on fracture toughness and fatigue crack propagation resistance. For this it was compared dual phase steels with different microstructures, mainly due to martensite content. Was performed an experimental analysis of the mechanical properties through tension, fracture toughness and crack propagation tests. Moreover it was used ABAQUS software to evaluate the material during the cracks propagation from experimental results, using the extended finite elements XFEM. The results shown that an increase of martensite phase on the dual phase steel microstructure decrease the fatigue crack velocity and increase their mechanical strength