ABSTRACT Name : Deliga Serpita Study Program : Dentistry Title : Study of Surface Roughness Between Heat Cured Acrylic Resin and Thermoplastic Nylon That Immersed in Ulee Kareng Coffee (Coffea robusta) Heat cured acrylic resin is material that mostly used as material of denture base in dentistry, nowadays thermoplastic nylon is also used. Denture base material has a physical properties, which one is surface roughness. Surface roughness can occur in heat cured acrylic resins and thermoplastic nylon, caused the exposure of material with a solution containing acid, which one is coffee. This study was conducted to determine the difference between the surface roughness of heat cured acrylic resins and thermoplastic nylon that soaked in Ulee Kareng coffee (Coffea robusta). There were 8 specimens, 4 Meliodent heat cured acrylic resin and 4 BIO TONE thermoplastic nylonwith a size of 20 x 20 x 2 mm.First initial surface roughness measurements on heat cured acrylic resins and thermoplastic nylon. The specimen is immersed in a solution of coffee for 4 days (simulate consume coffee solution for 1 year) with a solution of coffee replaced every day. Each specimen was immersed seen using a surface roughness tester Mahr. The results of data analysis showed that there are significant differences in surface roughness of heat cured acrylic resins and thermoplastic nylon after immersion in Ulee Kareng coffee (Coffea robusta) with unpaired t-test (p