To investigate the effects of customer involvement as an information source (CIS) throughout the innovation process, this study uses Korea Innovation Survey data and a two-stage data envelopment analysis method. The results are as follows. High-tech firms using CIS had lower R&D efficiency at the value creation stage. Low-tech firms using CIS had higher R&D efficiency at the value creation stage, but lower R&D efficiency at the invention stage. This paper's academic implication extends the research on CIS by examining its effects on firms' R&D efficiency. It also provides a practical guideline for firms that want to leverage customer knowledge.