The working model of type III gypsum is commonly used as working model for removable dentures. K2SO4 is well known as an effective accelerator to accelerate the gypsum setting time. This study aimed to identify the effect of K2SO4 1.5% solution on type III gypsum surface roughness. Surface roughness tests were performed using a Surface Roughness Tester at 1 hour, 24 hours, and 7 days after manipulation the gypsum. The results showed that type III gypsum surface roughness varied until the 7-day test. Moreover, the surface roughness of type III gypsum and K2SO4 1.5% solution is lower than type III gypsum surface roughness and equal to type IV gypsum surface roughness. It is concluded that the addition of K2SO4 1.5% solution decreased type III gypsum surface roughness.