In the repair process achieving high bond strength between the new and old resin based materials is necessary for clinical longevity. This study compared the effect of three different mechanical surface treatments (air abrasion, Nd:YAG laser and diamond bur) on the repair bond strength of giomer.In this in vitrostudy, 125 cylindrical giomer samples were used. The giomer samples were randomly assigned to 5 groups (n=25). In group 1, the samples did not undergo any surface treatment. In groups 2 to 4, the samples underwent surface treatments with air abrasion, Nd:YAG laser and a diamond bur. The samples in group 5 were prepared to measure giomer cohesive strength. Subsequently, the new giomer was bonded to the existing giomer in groups 1 to 4. Then the repair bond strength of the samples was measured. One-way ANOVA and post hoc Tukey test were used to compare the bond strength.There were significant differences between the different surface treatments (P<0.001); the repair bond strength in the air abrasion group was significantly higher than that in the Nd:YAG laser group, in which it was significantly higher than that in the diamond bur group, which was in turn higher than that in group 1 (no surface treatment) (P<0.001). In addition, the cohesive strength of giomer was significantly higher than the repair bond strength in the 4 other study groups (P<0.001).Of all the surface treatments, air abrasion and Nd:YAG laser, in descending order, yielded the highest repair bond strength values, with the repair bond strength values of 60‒70% of the giomer cohesive strength. Key words:Air abrasion, bond strength, giomer, Nd:YAG laser, repair, surface treatment.