•The self-healable glass fibers-epoxy composites were fabricated.•The composites containing 14 wt% microcapsules had optimum results.•The maximum healing efficiency in tensile strength was 97.5%.•The maximum healing efficiency in interlaminar shear strength was 144.5%.•The crack pining and deflecting by microcapsules were observed. In the present study, the self-ability based on the microcapsule healing system on the glass fibers-epoxy smart composites was investigated. The microcapsules’ shell and healing agent comprised urea-formaldehyde and diluted epoxy, respectively. The synthesized microcapsules by one-stage in-situ polymerization method were dispersed with the different percentage of 7, 14 and 21 wt% into the epoxy resin. Then, the epoxy-glass fibers composites with the self-healing ability were fabricated by hand lay-up method. The self-healing composites damaged by various damage forces through a quasi-static penetration method. Therefore, the damage forces of 800, 1050 and 1300 N for tensile samples and 2500, 2900 and 3300 N for interlaminar shear strength (ILSS) samples were selected. The obtained results showed that adding 14 wt% microcapsules into the composite increased the tensile strength, due to the crack pining and deflection mechanisms. Whereas, by increasing the percentage of microcapsules up to 21 wt%, the shear strength of composite was reduced, compared with the pristine composite. The maximum obtained healing efficiency for both tensile and ILSS tests were 97.5 and 144.5%, respectively, which belonged to 21 wt% microcapsules-loaded composite. The microscopically investigations of interactions between microcapsules and micro-cracks at the fracture surface illustrated the crack pinning, deflecting, and bowing mechanisms. Also, rupturing the microcapsules, wetting the damaged area by healing agent and forming the polymeric shell in the damaged area were seen.