Calcium sulfate whiskers are modified by three kinds of coupling agents. The modified calcium sulfate whiskers are then introduced into polypropylene to prepare calcium sulfate whiskers/PP composites. Mechanical strength tests show that notched izod impact of polypropylene increases dramatically by adding calcium sulfate whiskers. When a silicane coupling agent KH-570 is adopted to modify calcium sulfate whiskers at 30 % (w/w) of whiskers, the notched izod impact of composites can increase by nearly 60 %. SEM is utilized to observe the impact fracture surface morphology of the composites and the distribution of calcium sulfate whiskers in the PP matrix. The results indicate that the surface treatment can promote uniform distribution of calcium sulfate whiskers in the PP matrix, and improve the notched izod impact and toughness of composites. Coupling agents play a role in toughening for the calcium sulfate whiskers/PP composites.