Beginning in 2002, the regulations were changed to mandate the public disclosure of external auditor appointment and dismissal for companies listed on the Korea Stock Exchange and registered on KOSDAQ. This paper examines the impact of such auditor change announcements on the stock market, thereby investigating the effects of this regulation on the capital market. In this study, auditor changes were classified into upward changes, downward changes, and lateral changes based on audit quality, and stock price reactions were examined. Additionally, stock market reactions were reviewed according to the reasons for auditor changes. The results showed that the stock market exhibited an increasing trend in abnormal returns around the announcement date for upward auditor changes, while displaying a decreasing trend for downward auditor changes, with statistically significant results. For auditor change events resulting from disagreements between the firm and the external auditor, the average abnormal returns showed negative values on the event date and two days after, but these were not statistically significant. Firms that made downward auditor changes due to disagreements did not exhibit more negative stock price reactions than firms that simply made downward auditor changes, and the results were not statistically significant.