Purpose: To evaluate the effect of dentin treatment using HEMA phosphate (HEMA-P) on the microtensile bond strength (μTBS) and nanoleakage of an etch-and-rinse adhesive system. Materials and Methods: The occlusal surfaces of human molars were wet ground until superficial dentin was exposed. The specimens were then assigned to two groups according to dentin treatment: PA: 37% H₃PO₄ for 15 s; or HP: HEMA-P for 15 s. Adper Single Bond 2 was applied to the treated dentin surfaces and resin composite buildups were incrementally constructed over them. After 24-h storage in artificial saliva at 37°C, the bonded teeth were cut into resin-dentin sticks with a cross-sectional area of 1 mm², which were submitted to μTBS testing immediately or after 3 months of storage in artificial saliva at 37°C. Nanoleakage was assessed using SEM/EDS, and the interaction between dentin and H₃PO₄ or HEMA-P was evaluated by combining micro-Raman and FT-IR spectroscopy. The data were analyzed using two-way ANOVA and Tukey's HSD post-hoc test (α = 0.05). Results: HP presented significantly higher μTBS than PA at both times (p 0.05). Both treatments maintained μTBS stability after 3 months of artificial saliva storage (p > 0.005). At both times, PA presented higher nanoleakage than HP (p 0.05). Conclusions: Both dentin treatments maintained μTBS stability after 3 months of artificial saliva storage. The use of HEMA-P was associated with less nanoleakage than was traditional phosphoric-acid etching. Keywords: dentin bonding, dentin treatment, HEMA phosphate, microtensile bond strength, nanoleakage