This study attempted to analyze the impact of capital investment on firm value in the Korean capital market. To achieve this objective, the study was conducted as an event study examining stock price movements around the time when corporate capital investment decisions were publicly announced in the stock market. Additionally, to explain the effects of capital investment, theories on capital investment and firm value were reviewed, and regression analyses were performed based on several financial variables suggested by these theories. The results indicated that capital investment had a positive impact on corporate stock prices. In other words, capital investment by firms in the Korean capital market appeared to be undertaken with the objective of value maximization to enhance firm value. This evidence implies that managers convey new information about the firm's production and product demand—information not known to general investors—through investment decisions, and that this information is interpreted by investors as a favorable signal in evaluating firm value. However, such information appeared to be leaked prior to its official market announcement, suggesting that appropriate countermeasures are needed. Furthermore, operating performance and the ownership stake ratio of owner-managers emerged as important factors related to capital investment and firm value. Specifically, the greater the improvement in operating performance following capital investment, the greater the increase in firm value due to the investment, and the higher the managerial ownership ratio before the investment, the greater the increase in firm value resulting from capital investment—results consistent with prior research.