Objectives. The present study was intended to investigate the effect of different concentrations of chitosan nanoparticles mixed with an orthodontic primer on the shear bond strength and bond failure of stainless steel brackets bonded to dental enamel. Methods. Four concentrations of chitosan nanoparticles (0%, 1%, 5%, and 10%) were prepared and mixed with Transbond™ XT primer. Forty-eight extracted maxillary first premolars were bonded under a standardized procedure with stainless steel orthodontic brackets utilizing those different concentrations (12 teeth per each group). After the bonding procedure, the specimens were stored in deionized water (37°C for 24 hr) and then thermocycling 5,000 times before shear bond testing, which was performed using a universal testing device. Bond failure sites were examined under a stereomicroscope. Scanning electron microscopy and X-ray diffraction were also performed to verify and evaluate the phase of the nanopowder. Results. The data were statistically analyzed using one-way analysis of variance) and Kruskal–Wallis H tests, and the findings revealed statistically nonsignificant group differences regarding the shear bond strength and adhesive remnant index ( p > 0.05 ). Conclusions. Primers containing varying concentrations of chitosan nanoparticles demonstrated acceptable shear bonding strength and adhesive remnant index.