Background: Bulk-fill composites emerged to enable deep restorations in single placing. Although they seem promising, their aging must be investigated. Purpose: To evaluate the marginal microleakage of restorations made with bulk-fill and conventional composites, submitted or not to mechanical and thermal aging. Material and Methods: Five millimetres deep Class II cavities were restored with bulk-fill (Tetric N-Ceram Bulk-fill - TetricBF, Filtek Bulk-fill Posterior Restorative – FiltekBF, SonicFill - Sonic) or conventional composites (Filtek Z350 XT - FiltekZ, and Surefil SDR Flow as base + Filtek Z350 XT – SDR + FiltekZ). Mechanical and thermal aging were performed following the restoration. Teeth were allocated in 10 groups (n = 10) based on type of composite and performance or not of mechanical and thermal aging. Dental blocks of all group were immersed in 2% methylene blue solution. Marginal microleakage was analyzed through Spectrophotometry. Data were submitted to two-way ANOVA and post-hoc Tukey’s test. Results: FiltekZ presented highest microleakage, while TetricBF and FiltekBF showed lowest microleakage, regardless of being aged or not. Aged TetricBF and Sonic showed higher results of microleakage than not aged TetricBF and Sonic. Conclusions: Bulk-fill composites restorations presented lower marginal microleakage than conventional composite restorations. However, bulk-fill composites were more prone to the effects of aging than conventional composite.