Purpose: To evaluate the effect of different phosphoric acid concentrations (10% and 37%) on the microtensile bond strengths (μTBS) of three dentin adhesive systems with different solvents (ethanol, acetone, or none). Materials and Methods: Eighteen third molars divided into six groups were ground flat to expose superficial dentin, which was polished to 600-grit. The bonding procedure was initiated using either of two phosphoric acid gels (10% and 37%). Three adhesive systems - Single Bond (SB), Prime & Bond NT (NT), and One Coat Bond (CC) - with different solvents (ethanol, acetone, or none, respectively) were used. After adhesive application, a cylinder of composite resin was built up. After 24 h water storage, each tooth was serially sectioned into thin rectangular sections (or sticks) parallel to the long axis and with a mean cross-sectional area of 0.4 mm². μTBS were determined using an Instron universal testing machine. Data were analyzed using two-way ANOVA and Duncan’s test. Results: Mean bond strengths ranged from 66.1 MPa for 10% H₃PO₄ and SB to 43.8 MPa for 37% H₃PO₄ and OC. SB and OC tended to have slightly higher bond strengths when 10% H₃PO₄ was used. NT with 37% H₃PO₄ had a significantly higher μTBS (54.6 MPa) than NT with 10% H₃PO₄ (44.4 MPa). Conclusion: Etching dentin with 37% H₃PO₄ resulted in a significantly higher mean μTBS for the acetone-based adhesive NT. For both the ethanol- and water-based adhesive (SB) and the solvent-free adhesive (OC), acid concentration did not significantly affect bond strength.