Using IT investment data of 24 securities companies from 1992 to 2004 which are from Payment Systems & Treasury Service Department of the Bank of Korea, the effect of IT investments of securities companies on the profitability is analyzed. The IT investment proved to improve the profitability of all securities companies in consideration by pooled OLS model, random effects model, and fixed effects model. This positive effect of IT investments on the profitability of securities companies holds for big-sized securities companies. However, this effect is not detected for small- and medium-sized securities companies. These empirical results imply that, overall, the strategy of increasing IT investments by our securities companies has been desirable. However, small- and medium-sized securities companies may have to reconsider their IT investment strategies.