Voting premium includes not only the monetary benefits obtainable by exercising the voting rights but also the non-monetary value. The price difference between common and preferred stocks is mainly due to the difference in voting rights. The voting premiumvaries depending on the size of the private benefits of corporate control and the possibility of the competition in the control. Due to the agency problembetween controlling and non-controlling shareholders, the controlling shareholders pursue private benefits such as transferring wealth at the expense of the minority shareholders’ interests. As one of the corporate governance mechanisms, the audit committee has themost critical effect on corporate transparency bymonitoring corporate financial reporting and internal control. This study investigates the role of the audit committee in controlling voting premiums by analyzing how the existence and nature of the audit committee affect the voting premium. We focus on the supervisory role of audit committee that can mitigate the pursuit of private benefits by controlling shareholders andmanagers. For this purpose, this study conducted an empirical analysis using a sample 950 firm-years of listed companies in Korea Stock Exchange that issued preferred stocks during 2005-2015 period. for which relevant financial data are available. Empirical results are as follows. First, we find that companies with audit committees have higher voting premiums than those without audit committees. This finding is interpreted as that since audit committees have been installed by regulatory demands in Korea and do not have a practicalmonitoring function, they are unable to control the private benefits of the controlling shareholders. Second, as we separately tested audit committee characteristics represented by independence, expertise, and activity, we discovered that the voting premium is higher when the audit committee was composed entirely of outside directors. This may be due to the lack of enough time for outside directors to perform the monitoring function, and the audit committee may not work properly with such busy outside directors. Third, we tested the difference between audit organization with and without full-time auditors and find that the value of voting premium was higher for companies without full-time auditors. This result suggests that the non-full-time audit organization is vulnerable in information accessibility to the company’s daily works. Hence it may be ineffective to monitor and control the private benefits of the controlling shareholders. Empirical results provide insights into which institutional improvements are needed to enhance audit committee effectiveness. This study contributes to the existing literature in that it considers the new determinants of the voting premium, the existence and characteristics of the audit committee, which are not studied in the previous literature.