Abstract: Objective: To assess the effect of Streptococcus mutans invasion on the aging of four kinds of composite resin bonding interface. Methods: Two kinds of bulk-fill composite resins and two kinds of conventional composite resins were selected and immersed into bacterium solution for 14 days. After the specimen was subjected to ultrasonic cleaning, the bonding surface cracks were observed under a stereoscopic microscope, and the percentage of cracks areas were evaluated. Two samples in each group were then picked and sprayed using ion sputtering equipment. After fixed with conductive adhesives, the samples were observed under a scanning electron microscope. Results: Streptococcus mutans invasion led to different destruction of these composite resins bonding interface with no significant difference among the groups. According to the damage classification, SDR had the highest damage average, and the damage average of Z350 was slightly higher than that of P60 and Tetric N-Ceram Bulk Fill. The damage was located between the bonding surface and the dentin of P60 and Tetric N-Ceram Bulk Fill, while between the adhesive surface and the resin of Z350 and SDR. Conclusion: Streptococcus mutans can damage the surface and bonding interface of composite resin in a short time. Different resin components exhibited different failure modes, but showing no significant difference in the extent of damage.