Analyzing data from Chinese online interactive investor platforms, our study reveals that Minority Shareholder Activism (MSA) effectively curtails informed insider trading by voting with their hands or feet, particularly in firms with weaker external monitoring. MSA not only reduces the profitability of insider trading but also encourages firms and regulators to implement stricter ex-post disciplinary measures. Moreover, MSA alleviates the negative impact of insider trading on the stock market by enhancing stock liquidity, increasing stock price informativeness, and reducing crash risk.