This paper inquires into the causal relationship between R&D investment and GDP (Gross Domestic Product) in Korea. We apply the method of unit-root test, co-integration test, and Hsiao version of the Granger causality test to find the evidence of bi-directional causality between R&D and GDP. However, it is interesting to observe no significant directional effect between government funded R&D and GDP while private sector funded R&D turns out to affect GDP significantly. Utilizing the previous study results on bi-directional relationship between government and private sector funded R&D, we draw the following conclusion: In order to increase GDP, government funded R&D needs to induce private sector to fund more R&D in an effective manner. In this way, government is expected to indirectly participate in the development for better economy in Korea.