Objective: To evaluate the effect of different surface treatments on shear bond strength (SBS) between bulk-fill resin composite (BFRC) and bulk-fill flowable resin composite (BFFRC) or conventional flowable resin composite (CFRC). Materials and Methods: Sixteen blocks were prepared from Tetric N-Ceram BFRC, aged by thermo-cycling, and then stored in artificial saliva for 6 months. The blocks were divided into 4 groups (n=4) according to the surface treatment; Group1:  roughened by coarse discs, Group 2: roughened by coarse discs and silanization, Group 3: roughened by air abrasion, and Group 4: roughened by air abrasion and silanization. Each group was subdivided into 2 subgroups (n=2) according to the used repair restorative system; subgroup A repaired with Tetric N-Bond universal adhesive/ Tetric N-Flow BFRC, and subgroup B was repaired with Prime& Bond universal adhesive /Spectra ST flow CFRC. The repair RC was placed on the RC blocks using tygon tubes and cured. The specimens were tested for SBS using a universal testing machine. Results: Regarding the effect of different surface treatments for both repair restorative systems, there was a significant difference (P<0.001). Regarding the effect of silane, there was no significant difference (p= 1.00). There was no significant difference between repair with CFRC or BFFRC (P =0.679). Conclusions: Surface treatment by air abrasion followed by silane and universal adhesive can be attempted clinically for the repair of aged BF restoration. The aged BFRC could be effectively repaired with the same bulk-fill or conventional RC if proper repair protocol was used.