Medical problems such as gastroesophageal reflux disease can cause considerable damage to restorations in the oral environment. This study evaluated the effects of gastric juice on the surface characteristics of different types of laboratory-processed indirect composites with different filler particles and polymerization modes. Specimens were prepared from Tescera (TES; Bisco), Sinfony (SIN; 3M ESPE), Solidex (SOL; Shofu), and Adoro (AD; Ivoclar Vivadent). Before exposing the specimens to simulated gastric juice for 24 h, color, surface roughness, and microhardness were measured on one half of the polished flat surface of each specimen. After exposure to the simulated gastric juice, the same tests were repeated on the other half of specimen surface. Results indicated that gastric juice had a significant impact on color change (p<0.001). AD showed the largest surface roughness change among the resins (p<0.001). Gastric juice also significantly affected the microhardness of the materials, and AD and TES showed statistically similar change in microhardness (p>0.05).