Aim: The aim of the study was to evaluate the effect of surface treatments on the repair ‎shear bond strength of aged ORMOCER resin composite. Materials and Methods: 12 discs ‎of ORMOCER based resin composite were divided into 6 groups (n = 2 discs/group) as per ‎the surface treatments performed as follows: 1-Medium grit diamond Bur+Universal ‎Adhesive. 2-Fine grit diamond Bur + Universal adhesive. 3-Air abrasion+ Universal ‎adhesive. 4-Air abrasion+ Silane+ Universal adhesive. 5-Etchant + Universal adhesive. 6-‎Etchant + Silane + Universal adhesive. Each disc received five micro-cylinders of flowable ‎nanohybrid resin composite repair material then subjected to micro-shear bond strength ‎testing using a universal testing machine. Results: There was a significant difference ‎between different groups (f=4.47, p=0.002). The highest bond strength was found in group ‎‎(II) (28.74±4.18) (MPa), followed by group (IV) (25.00±5.09) (MPa), then group (VI) ‎‎(23.36±5.08) (MPa), group (III) (22.07±5.30) (MPa) and group (I) (21.57±7.64) (MPa), ‎while the lowest bond strength was found in group (V) (18.09±4.04) (MPa). Post hoc ‎pairwise comparisons showed group (II) to have significantly higher values than groups (I) ‎and (V). Conclusion: The best surface treatment for repair of an aged ORMOCER based ‎resin composite could be the use of fine diamond bur with universal adhesive, followed by ‎air abrasion with or without silane. Silanation is an essential step with acid etching while ‎repairing ORMOCER based resin composite.‎