PVC/BaSO4 composites were prepared by melt blending method. The mechanical properties, microstructure and thermal stability of the composites were investigated. The results indicated that BaSO4 decreased the tensile yield stress and improved the elongation at break of PVC composites. Ductile fracture characteristics such were observed in the tensile fracture surface of PVC/BaSO4 composites. The toughening mechanism was cavitations toughening mechanism and shear zone toughening mechanism. The reaction of dehydrochlorination was limited by the addition of BaSO4.