Purpose: The aim of this study was to evaluate the effect of different cavity disinfectants on dentin bond strengths ofcomposite resin applied with two different adhesive systems. Materials and Methods: One hundred mandibular third molars were sectioned parallel to the occlusal surface to expose midcoronal dentin. The dentin surfaces were polished with waterproof-polishing papers. The specimens were randomly divided into 5 groups of 20 each. In group 1, the specimens were not treated with any cavity disinfectants and served as control. From groups 2 to 5, dentin surfaces were treated with the following cavity disinfectants, respectively; 2% chlorhexidine solution, 2.5% NaOCl, 1% chlorhexidine gel, 3% H2O2. The specimens were then randomly divided into 2 subgroups including ten teeth each to evaluate the effect of different bonding systems. Dentin bonding systems were applied to the dentin surfaces and the composite buildups were created. After the specimens were stored in an incubator for 24 h, the shear bond strength was measured at a crosshead speed of 1 mm/min. The bond strength data were analyzed with one way analysis of variance and Tukey-HSD tests. Results: There was no significant difference between chlorhexidine gel and control groups regardless of the type of the bonding agent (p > 0.05). On the other hand, pretreatment with NaOCl, H2O2 or chlorhexidine solutions had a negative effect on the shear bond strength of self-etching bonding systems. Conclusion: The findings of this study suggest that when NaOCl, H2O2 or chlorhexidine solution are used as a cavity disinfectant, an etch-and-rinse bonding system should be preferred. Schlagwörter: bond strength, adhesive, composite resin, cavity disinfection, CHX gel