Corporate transparency is directly related to managerial moral hazard, agency costs, transaction costs in financial markets, and adverse selection problems for the firm itself, and these are directly connected to firm value. Furthermore, corporate transparency is deeply related to corporate social responsibility. This is because corporate opacity not only reduces the overall utility of society but also undermines fundamental national competitiveness and hinders sustainable development. Despite this importance, however, empirical analyses of firm value or economic performance in relation to corporate transparency have been scarce both domestically and internationally, due to data limitations in measuring corporate transparency and the underdevelopment of transparency indices. Therefore, this study aimed to directly develop and measure a transparency index and analyze the impact of the transparency index on firm value. To measure the transparency index, objectively disclosed information from approximately 1,600 firms listed on the Korea Stock Exchange and registered on the KOSDAQ market as of 2003 was utilized. For index development and measurement, the index was first divided into four transparency domains: ownership structure transparency, business status transparency, board of directors transparency, and accounting transparency. A total of 104 survey items were developed for these domains. These 104 items were classified as '0' or '1,' summed, and expressed as percentages, ultimately indexing the degree of transparency for 1,271 firms. Based on this index, the impact of corporate transparency on firm value was analyzed using multiple regression analysis with White Heteroskedasticity-Consistent Standard Errors and Covariance. The results showed that transparency affects firm value. Specifically, the overall transparency index, along with ownership transparency, board transparency, and accounting transparency, were shown to be statistically significantly positive at least at the 10% level. However, the results showed no statistical significance with general measures of corporate economic performance, namely return on investment (ROI), return on total capital operating profit (ROM), and return on assets (ROA) measured by net income. This can be interpreted as meaning that while transparency does not guarantee a firm's economic performance, being transparent ensures that the firm is properly evaluated in the market and thereby enhances firm value.