The purpose of this in vitro study was to investigate the effects of water-jet flossing on the color stability and surface roughness of five resin-based composites. Five commercially available composite resins were studied. Nine disc-shaped specimens (6x2mm) were fabricated from each composite. The specimens were randomly allocated into three groups and three different treatments were performed on each group: storage in water (control group), water-jet flossing using 50 Psi water pressure, and water-jet flossing using 100 Psi water pressure. The water-jet flossing was performed in a standardized manner using a Waterpik® Aquarius® water flosser. Color and roughness were measured at baseline and at the end of 30 minutes of treatment, which is approximately equivalent to 5 years of simulated water-jet flossing for 1 minute once a day. The data were statistically analyzed using two-way analysis of variance (ANOVA) with Bonferroni and Tukey?s post-hoc tests. No significant color change was found after 5 simulated years of water-jet flossing, irrespective of composite type and water-flossing pressure setting (p > 0.05). Furthermore, none of composite specimens showed any significant surface roughness changes except for the two composites with spherical filler specimens in the 100 Psi treatment group. These composites exhibited a significant increase in surface roughness compared with the nano-filled composite (p = 0.001 and p = 0.006). However, the differences were clinically acceptable (?0.2 µm). In terms of surface roughness and color, water-jet flossing is safe to be used on composite restorations within the settings of this study.