Abstract: Series of magnesium oxysulfate/polypropylene (MOS/PP) composites magnesium oxysulfate particle (MOS_P), magnesium oxysulfate whisker (MOS_W), and magnesium oxysulfate sector (MOS_S) were prepared via melt blending method using magnesium oxysulfate (magnesium oxysulfate particle (MOS_P), magnesium oxysulfate whisker (MOS_W), and magnesium oxysulfate sector (MOS_S)) as fillers, lauric acid (LA) as modifier and PP resin as the matrix. SEM results indicate that both modified MOS_P and MOS_W are fine dispersed in the PP matrix, whereas the incompatibility issue still exist. For MOS_S/PP composites, MOS_S with huge size and complicated morphology and partial dispersed MOS_W are coexisted, with more interface defects observed. Wide angle X-ray diffraction (WXRD) results suggest that addition of MOS can induce the formation of β-crystal PP which is irrelevant to LA, especially for the MOS_P/PP sample. The incorporation of three kinds of MOS slightly decreases yield strength of the PP matrix. One reason is the incompatibility between MOS and the PP matrix, and the formation of β-crystal is another important reason. In contrast, introducing MOS_W can maintain the yield strength and tension fracture toughness and reinforce the modulus of PP matrix obviously, which is mainly due to the high aspect ratios of whisker morphology. In addition, the most obviously toughening effect happens on the MOS_P/PP composites for two reasons. On the one hand, MOS_P is more efficient for inducing β-crystal PP as compared with MOS_W and MOS_S. On the other hand, the more fatty acid salt attached to the surface of MOS_P results in the stronger plastification effect to the PP matrix.