OBJECTIVE Restorative materials may be exposed in the oral cavity to chemical agents found in beverages, which may lead to their biodegradation. The purpose of this in vitro study was to evaluate the effect of two fruit drinks commonly used by children on surface roughness of two esthetic restorative materials. METHODS One resin composite (RC), one resin-modified glass ionomer (RMGI) and two fruit drinks (orange and cocktail) were used in this study. Specimens (n=20) of each material were fabricated against Mylar strip. Baseline measurements of surface roughness were recorded for each group using noncontact surface profilometer. Each specimen was placed in the tested fruit drinks for 24 hours and then surface roughness was recorded. RESULTS The mean (±SD) surface roughness of RC before and after immersion in orange and cocktail were 0.04±0.02, 0.12±0.05, 0.06±0.03 and 0.11±0.06, respectively and for RMGI were 0.72±0.14, 0.60±0.19, 0.56±0.11, and 0.52±0.15. For RC there was significant difference between surface roughness (Sa) before and after immersion in orange and cocktail (P<0.05). For RMGI, there was significant difference between surface roughness before and after immersion in orange (P<0.05), but no significant difference before and after immersion in cocktail (P>0.05). CONCLUSIONS The surface roughness of the RC and RMGI examined showed a significant change in the surface roughness after immersion for 24 hours in the tested fruit drinks.