Abstract: A hybrid joint with a satisfactory mixture of pure magnesium and polypropylene (PP) was achieved via friction stir joining (FSW) in a lap-joint configuration. The tool rotational and travel speeds used in this work were 500-700 r/min and 50-100 mm/min, respectively. The mechanical properties and microstructural analysis of the resultant hybrid Mg/PP joint were examined. The results show that the maximum tensile shear strength (22.5 MPa) of the joint was attained at 700 r/min and 75 mm/min due to the optimum percentage fraction of mechanical interlocking (48%) and the presence of magnesium oxide. The interfacial joint center exhibits the maximum microhardness values because of the presence of refined and intertwined Mg fragments and density dislocations in the matrix of the PP. The joint failed via two different modes:interfacial line and weld zone fractures, respectively.