This paper analyses the effects of R＆D investment on patent in Korean manufacturing firms during the period 1984-99. The data contains 140 companies which listed in Korea Stock Exchange(KSE). We observed that the relative shares of R＆D investments and patent applications are much higher in scientific firms than in the other firms. The regression results show that R＆D investment has significantly positive effects on the growth of patent application and registration. And the effects of R＆D on patent turns out to be stronger in scientific firms than the other firms. The firm size and the capital intensity also have an important effect on the propensity to patent.