In this study, mechanical and thermal properties tests were performed on 0, 5, 10, 15, 20 and 25 wt% calcium sulfate whisker (CSW) filled poly (vinyl chloride) (PVC) (blended by twin-stator elongational rheologial extruder) to identify the effect of CSW weight fraction on the properties of PVC. The binary blends were characterized in terms of thermal (glass transition temperature) and mechanical properties. Their thermal stability was investigated by thermogravimetric analysis (TGA). Results indicated that the incorporation of CSW in PVC (matrix) increased thermal stability of the bioblend. Mechanical properties and microstructures were also studied. With the increasing of CSW, the tensile strength increased, as well as the tensile modulus. Meanwhile, a short increase followed by a rapid decrease were observed on the impact strength. SEM revealed the microscopic factors for this variation trend.