SUMMARY Objectives: This study aimed to evaluate the hydrolytic degradation ( in vitro ) and biodegradation ( in situ ) of different resin composites: bulk-fill (XTra Fill, XTF/VOCO; Tetric EvoCeram Bulk Fil, TBF/ Ivoclar Vivadent), self-adhering (Vertise Flow, VTF/ Kerr; Fusio Liquid Dentin, FUS/ Pentron Clinical), and a conventional resin composite (Filtek Z250, Z250/ 3M ESPE), which was used as a control. Methods and Materials: Seventy-five cylindrical specimens (7 × 1 mm) were desiccated and immersed into distilled water (DW), artificial saliva (AS), and 0.1 M lactic acid (LA) (n=5) for 180 days. Specimens were weighed after 180 days, after which they were desiccated again. The sorption (μg/mm 3 ) and solubility (μg/mm 3 ) were calculated based on ISO 4049. For the in situ phase, an intraoral palatal device containing five cylindrical specimens (5 × 1.5 mm) was used by 20 volunteers for seven days. Surface roughness was evaluated before and after this period to analyze the superficial biodegradation. Sorption and solubility data were submitted to Kruskal-Wallis and Mann-Whitney tests. The Wilcoxon signed-rank test was used to compare roughness at different observation times. The statistical significance for all tests was considered α =0.05. Results: For in vitro , self-adhering resin composites (VTF and FUS) showed, respectively, higher sorption values independent of the solution (62.55 and 50.81 μg/mm 3 in DW, 67.26 and 50.46 μg/mm 3 in AS, and 64.98 and 59.86 μg/mm 3 in LA). Self-adhering VTF also had a greater solubility value in DW (22.18 μg/mm 3 ) and FUS in LA (65.87 μg/mm 3 ). In AS, the bulk-fill resin composite XTF showed higher solubility (22.13 μg/mm 3 ). All resins were biodegraded, but the XTF specimens were more resistant ( p =0.278) to chemical attack. Conclusions: The self-adhering resin composites showed the highest hydrolytic degradation, and the bulk-fill resin composites exhibited comparable or superior results to the conventional resin composites. Not all resin composites underwent biodegradation in the in situ environment. The storage environment influenced the final characteristics of each material tested.