In this study, the enhancement of the failure loads of adhesive double-strap joints improved by nano-silica added in different concentrations is investigated. An epoxy-based structural adhesive, Araldite 2011, improved by silica nanoparticles through a course of actions, is utilized to attach aluminum adherend. Nano-silica in different concentrations is added to the adhesive so as to find the optimum weight percentage and to provide a comparison with previous studies. Manufactured specimens are tested under tensile loading in order to find the failure load of the joints. Afterward, images taken by scanning electron microscope are utilized to survey the quality of nanoparticles dispersion as well as the cause of the augmentation in the failure load. The results reveal a maximum enhancement of 21% in the failure load when the weight percentage of the nano-silica is 2 wt%. In addition, the postponement of the crack propagation is found out as a key factor in improving the failure load.