Objective: To evaluate the antibacterial activity of adhesive resin incorporating chitosan as well as the adhesive characteristics. Method and Materials: An experimental adhesive was prepared by adding 0.12%, 0.25%, 0.5%, and 1% (w/w) chitosan solution to Single Bond adhesive resin. The solution of chitosan was prepared by dissolving 2 g of chitosan powder in 1 liter of 1% (v/v) acetic acid. Single Bond without chitosan was used as a control. The antibacterial activity was evaluated using a direct contact test against Streptococcus mutans. The viscosity, degree of conversion, pH, and microtensile bond strength (µTBS) values of the experimental adhesives to dentin were evaluated. Data were analyzed using the ANOVA and Tukey tests. Statistical significance was set at the .05 probability level. Results: The antibacterial properties of freshly prepared and aged experimental adhesives incorporating chitosan were found to exhibit an inhibitory effect on the growth of Streptococcus mutans compared with the unmodified adhesive resin (P .05). The viscosity of the experimental adhesives increased with increasing the concentrations of chitosan incorporation into the adhesive. However, the degree of conversion and pH values decreased with increasing the concentrations of chitosan incorporation into the adhesive. Experimental adhesives incorporating 0.12% and 0.25% (w/w) chitosan showed no significant differences in the µTBS values compared with the control (P > .05). However, the incorporation of 0.5% and 1% (w/w) chitosan into the dental adhesive significantly decreased the µTBS (P .05). Conclusion: Adhesive resin that contains 0.12% (w/w) chitosan is a promising antibacterial adhesive that does not adversely affect adhesive properties. Keywords: adhesive properties, antibacterial activity, chitosan, dental caries, microtensile bond strength, viscosity