Abstract This research was carried out to investigate the influence of different concentrations of Mn (0.5, 1, 2, 3 and 5%) on the microstructure and tensile properties of Al–15wt.%Mg2Si metal matrix composite. Microstructural examination was carried out using optical and scanning electron microscopy (SEM). The results depicted that 1wt.% Mn addition changes the morphology of primary Mg2Si from irregular to polyhedral shape and its average particle size decreases from 40μm to 12μm. Cubic morphology of particles was also observed by the addition of 2% Mn. Further addition of Mn (>2%) did not significantly change the size or morphology of the primary Mg2Si. Microstructural studies also showed that Mn addition changes the morphology of the eutectic Mg2Si phase from flake-like to rod-like. Tensile properties of specimens with different Mn contents were also investigated. The results of tensile testing revealed that optimum Mn level for improving both UTS and elongation values is 2wt.%. At higher Mn concentrations, an intermetallic phase (Al6Mn) introduced on eutectic cell boundaries appears to be the main reason for slight reduction in tensile properties. A study of the fracture surfaces via SEM revealed a brittle mode of failure in Mn free composite. However, the addition of 2wt.% Mn changes the fracture mode to ductile by increasing fine dimples and reducing the number of decohered particles thereby increasing the composite ductility.