The purpose of this study was to investigate the effect of various dentin acid treatments on the tensile bond strength of resin composite to dentin, mediated by Prisma Universal Bond 2. Acid solutions (maleic acid, Na-EDTA, phosphoric acid, citric acid/ferric chloride) were applied to dentin surfaces for 15 seconds or 60 seconds, and tensile bond strengths evaluated. For all acids, there was a significant difference in bond strength for the two treatment times; for phosphoric acid and citric acid/ferric chloride, the 15-second application resulted in a higher bond strength, while the reverse was true for Na-EDTA (sodium-EDTA) and maleic acid. The highest bond strength (19.6 MPa) was associated with 15-second citric acid/ferric chloride application, and the lowest bond strength (5.6 MPa) with 60-second application of citric acid/ferric chloride. The bond strengths with 60-second citric acid/ferric chloride (5.6 MPa), 15-second Na-EDTA (5.8 MPa), and 60-second phosphoric acid (6.3 MPa) were not significantly different from the control (5.7 MPa).