This paper explores how state ownership and policy reform affect the internal efficiency of corporate social responsibility (CSR) in Chinese firms. Empirical results show that CSR improves financial and stock price performance for both private and state-owned firms. Before the CSR policy reform, state ownership weakens CSR's positive effect on financial performance while strengthening that on stock prices. After the government tightened the CSR requirements further in early 2013, state ownership simultaneously weakens CSR's positive impact on financial performance and stock prices, implying that state-owned firms pay excessive internal costs to follow the government's stricter CSR requirements for external benefits.