Kawasaki Heavy Industries (KHI) developed an innovative robotic Refill Friction Stir Spot Joining (RFSJ) system for welding aluminum alloys. This RFSJ method, also referred to Refill Friction Stir Spot Welding (RFSSW), has been demonstrating a potential to replace solid rivets of aircraft structures. The aerospace industry uses riveting as a standard fastening method as it meets the baseline requirements and has well established standards and specifications. Riveting does not alter the microstructure of the material and can join either similar or dissimilar materials. However, the riveting process consists of labor-intensive steps, such as drilling, deburring, fastener insertion, and clenching, which burden the entire assembly process. Furthermore, riveting produces uneven joint surfaces due to the protruding rivet end(s) that may cause not only air turbulences but also aesthetic issues. The goal of this project is to investigate whether RFSSW indeed has a potential to replace solid rivets of aircraft structures. This study used an RFSSW tool and a solid rivet with similar sizes to compare RFSSW to riveting. The two joining methods were compared in terms of the mechanical properties of the joints made by the two methods. Mechanical tests, such as static and fatigue tests, were carried out to identify the mechanical properties in accordance with industrial standards and specifications. Statistical analyses were performed on the mechanical test results. The t-test analysis indicates there is a statistically significant difference between the failure loads of welded and riveted coupons. The welded coupons demonstrated significantly higher ultimate lap-shear strengths but slightly lower ultimate cross-tension strengths than that of the riveted ones. The fatigue test results indicate that the welded and riveted coupons demonstrated comparable low-fatigue-load strengths in the lap shear direction. However, welded coupons outperformed the riveted ones on high- fatigue-load lap shear tests.