Corporate boards of directors choose an innovative and important investment decision-making including R&D investments. The soundness and effectiveness of corporate boards depend upon the way how corporate boards of directors are composed and operated. Since corporate boards take risky and costly investment options, the composition and risk-taking of corporate boards attracts great attention from both home and international academics. We explore the association between the insider ratio and investment decisions. Prior literature provides many evidences on managerial risk aversion. We expect that firms with a greater insider ratio are likely to undertake more conservative and less risky investment projects, consistent with the managerial risk aversion hypothesis. In this paper, we expect a negative association between the insider ratio and investments in intangible assets such as R&D investment. Our evidence appears to support the managerial risk aversion hypothesis, since firms with a greater insider ratio have shown to have significantly reduced investments in R&D projects.