Research has argued that state-owned enterprises (SOEs) should bear more social responsibility than other listed firms, because their own goals include maintaining social stability and promoting social welfare. In contrast with the privatization of SOEs observed in other countries, in China, some listed firms’ major shareholders have become SOEs in recent years. This transition offers a good opportunity to investigate the impact of ownership change on firms’ corporate social responsibility (CSR). Using the propensity score matching difference-in-differences method, we document that the CSR performance of these firms does not improve when their ownership structure changes, and it can even worsen. Our results remain robust to a series of tests. Further investigating the underlying economic mechanism, we uncover those political connections, bank financing, and government subsidies play critical roles in determining the negative effect of ownership structure change on public firms, which is consistent with the soft budget constraint framework. In an additional analysis, we find that CSR performance is poor for manufacturing industry firms after ownership structure change. After calculating the frequency of keywords appearing in the annual reports of such firms, we find them to be satisfied with their new SOE background after ownership structure change. Our paper provides a possible explanation for the phenomenon of SOEs becoming major shareholder of listed firms.