Purpose: The aim of this study was to evaluate the influence of ultrasonic treatment on the bond strength of glassionomer cements to dentin. Materials and Methods: Conventional (Fuji II: a; Ketac-Fil Plus: b), resin-modified (Fuji II LC Improved: c; Photac-Fil Quick Aplicap: d), and more viscous conventional (Ketac Molar: e) glass-ionomer cements were tested. Fifty human molars were sectioned mesiodistally, embedded in epoxy resin with exposed buccal or lingual surfaces, and ground to obtain a flat dentin surface. A matrix with a central orifice in the shape of an inverted truncated cone was built with a bovine tooth and positioned on the dentin surface. In the control groups, the materials were inserted into the matrix. In the test groups, the ultrasonic treatment was applied to the surface of the matrix and the surface of the glassionomer cements. The specimens were stored in deionized water for 24 h at 37°C and subjected to bond strength tests. Data were analyzed using two-way ANOVA and Tukey's tests. Results: The mean bond strengths in MPa for the control groups were: a: 2.21, b: 1.85, c: 8.65, d: 5.93, and e: 2.10. The results for the test groups were: a: 3.33, b: 2.19, c: 9.95, d: 6.10, and e: 2.65. Ultrasonic treatment statistically increased the tensile bond strength of all tested cements (p 0.05). Conclusion: Ultrasonic treatment improved the bond strength of the glass-ionomer cements to dentin after 24 h. Keywords: ultrasonics, glass-ionomer cements, dentin, tensile strength