This paper investigates the impact of interorganizational learning on the innovation performance of R&D collaborations among different organizations. Although existing studies examined the reasons why some R&D collaborations are more successful than others, only a few studies have discussed the importance of the learning processes in partnerships at the inter-firm level. Drawing on the theories of interorganizational learning and social capital, this study extends the discussion on the performance effect of interorganizational learning in R&D collaborations and the role of social capital in the relationships among collaborating firms. Our analysis is based on an online survey conducted on a sample of Korean small and medium-sized enterprises (SMEs) that engaged in R&D collaborations. Our results show that firms that actively participate in interorganizational learning achieve better innovation performance through R&D collaborations. Furthermore, our findings indicate that the higher the social capital among R&D partners, the more the collaborating companies benefit from interorganizational learning in terms of innovation performance. These findings imply that interorganizational learning and social capital at the inter-firm level should be regarded as strategic elements for successful R&D collaborations. Beyond these implications, this study also confirms the catalyst role of social capital in the interorganizational learning process.