The present work aims at investigating the effect of adhesive modification on the lap shear strength of the adhesively bonded joints. The epoxy-based adhesive is reinforced with reduced graphene oxide (rGO) at different weight fractions. Single lap joints (SLJ) have been prepared by considering the commercially available aerospace-grade aluminum alloy AA8011 as the adherend material and Araldite 2014 A/B as the adhesive. Experiments showed that the addition of 0.5 wt.% graphene to the epoxy adhesive resulted an approximately 27% increase in the lap shear strength of the SLJ. Further increase in the reinforcement loading decreases the lap shear strength due to the agglomeration of graphene particles. A detailed analysis of the effect of reinforcement loading and overlap length on the shear strength has been presented and failure mechanisms are discussed.