Informal institutions are found to shape the behaviors of economic organizations within the business world by creating localized social norms and moral commitments. However, the existing literature pays greater attention to the financial consequences of such institutions, and little is known about their environmental impacts, especially in the context of transition economies. By linking institutional theory with environmental strategy literature, in this study, we develop a theoretical framework and empirically test how social trust, one of the dimensions of informal institutions, (...) influences corporate environmental responsibility. Using a longitudinal data set of Chinese listed firms from 2006 to 2015, we find support that firms located in regions with a higher level of social trust engage in more environmental responsibility activities. We also show that this effect is more pronounced when local environmental protests are fewer and information transparency is worse. Our findings highlight the importance of social trust in environmental governance and provide evidence of how it serves as a substitute for formal environmental institutions in transition economies. (shrink)