When a firm is controlled by a large shareholder, the principal agency problem arises from expropriation by controlling shareholders of other shareholders. Using a sample of 3776 publicly traded firms in the Chinese A-share market over the period 2007–2020, this study investigates whether stock liquidity impedes or enhances the expropriation behavior of controlling shareholders. I demonstrate that (1) a liquid stock market generally encourages expropriation behavior by controlling shareholders, (2) the positive effect of stock liquidity on expropriation by controlling shareholders is mitigated when active investors hold a large stake in the firm, and (3) active investors’ monitoring of expropriation by controlling shareholders is mitigated at state-owned enterprises and firms that have a large gap between ownership and control. However, higher competition among blockholders strengthens the discipline of active investors with respect to expropriation. This study builds a new link between a market factor (stock liquidity) and a governance problem (expropriation by controlling shareholders) and reveals some new characteristics in the relationship between stock liquidity and corporate governance in an emerging market. •High stock liquidity facilitates the entry of investors.•Active investors monitor the expropriation behavior by controlling shareholders.•Competition among blockholders enhances active investors’ monitoring.