Abstract: Maleic anhydride grafted ethylene-vinyl acetate copolymer (EVA-g-MAH) was used to toughen the calcium sulfate whiskers (CaSO_4W)/nylon6 (PA6) composites. The CaSO_4W/PA6 and CaSO_4W-(EVA-g-MAH)/PA6 composites were prepared using by a twin screw extruder, and analyzed by means of SEM, DSC, XRD and mechanical testing. The results indicate that addition of small amounts of CaSO_4W can increase the rate of crystallization, however, higher CaSO_4W contents lead to a decreased rate of crystalization and promotion of forming γ-crystals of PA6. Adding 10% (mass fraction) CaSO_4W increases both the stiffness and toughness of PA6. Adding 30% CaSO_4W can further improve the stiffness but significantly decreases the fracture toughness of PA6. With 2.5% and 5% mass fraction of EVA-g-MAH, the impact strength of 30%CaSO_4W-(EVA-g-MAH)/PA6 increases by 25.0% and 76.7%, respectively, thus imparting the higher toughness to the 30%CaSO_4W/PA6. The improvement of impact strength of the composites mainly results from energy-absorption process, effective stress transfering, the increasing in interfacial adhesion between CaSO_4W and PA6 in the presence of EVA-g-MAH as well as good miscibility of EVA-g-MAH/PA6 blend system.