Microstructure-based finite element modeling was performed on different microstructures of an austenitic-ferritic cast duplex stainless steel using the constitutive behavior of individual phase obtained from micropillar compression tests. A qualitative analysis of equivalent plastic strain and von Mises stress was conducted in plane stress and plane strain conditions. The simulated results reveal that the morphology and the area fraction of the second phase can affect the mechanical properties. The stress values and the equivalent plastic strain in the shear bands are higher in plane strain loading than plane stress loading condition. Stress is concentrated mostly in ferrite phase. The evolution of stress during deformation is found to be dependent on the morphologies of ferrite phase in austenite matrix.