Recognizing the lack of empirical studies on the returns to R & D investment in Korean firms, this paper analyzes the relationships between R & D investment and corporate performances measured by sales growth rate, profit rate and PER. The data used here are from 167 firms in 8 different industries covering the period from 1985 to 1989. The results show that the profit rate is strongly correlated with R & D investment. But unlike the results of most studies previously done in the U.S., R & D investment only weakly and insignificantly correlated with sales growth and PER.