Purpose: The aim of this study was to investigate the effect of Er;Cr;YSGG laser treatment with different energy levels before sandblasting and grinding on the transverse strength of denture base resin repaired with autopolymerizing resin. Material and Methods: A total of seventy rectangular specimens (65X10X3.3 mm) were prepared from heatpolymerized acrylic resin, which was repaired with autopolymerizing resin following conditioning methods: a) without surface treatment (control) b) grinding, c) sandblasting, d) Er;Cr;YSGG laser at 3 W-20 Hz + grinding, e) Er;Cr;YSGG laser at 3 W-20 Hz + sandblasting, f) Er;Cr;YSGG laser at 4 W-20 Hz + grinding, g) Er;Cr; YSGG laser at 4 W-20 Hz + sandblasting. The transvers strength was measured by a three-point bending test using a universal testing machine. Data were analyzed using 1-way ANOVA and Tukey’s Post Hoc test (p<0.05). Results: Er;Cr;YSGG laser application at 4 W-20Hz before sandblasting occured significantly higher values (30.48±7.66 MPa) when compared to the control group (15.48±4.32 MPa) (p<0.001). Grinding demonstrated the lowest values (9.38±4.62 MPa) among all the groups. Sandblasting showed significantly higher values than grinding (p<0.01). Laser application at 4W-20 Hz + sandblasting demonstrated significantly higher strength values than sandblasting alone (p<0.05). Conclusions: Surface pretreatments before repairing significantly affect the transvers strength of repaired denture base resin. Er;Cr;YSGG laser pretreatment at 4 W-20Hz before sandblasting may be useful to increase the transvers strength of denture base repairs