Corporate environmental responsibility (CER) can benefit our societies and enterprises. Understanding firms’ influencing factors of CER is essential to promoting CER. Recently, the literature has paid much attention to the impact of corporate political connections on CER. However, most studies on this topic were in the Chinese context, which cannot be generalized to every context. This study examines the impact of corporate political connections on CER in the Vietnamese context using panel data of small and medium-sized enterprises in the manufacturing sector from 2011 to 2015. The study employs various methods, such as the fixed-effect, the fixed-effect Poisson and the fixed-effect negative binomial methods for count data, the fixed-effect, the random effect and the pooled OLS methods for continuous data, and the fixed effect two-stage least squares method and propensity matching method to address the endogeneity of political connections. The paper finds that politically connected firms do CER as much as non-connected firms. In addition, the study also finds no heterogeneity in the effects of political links on CER in different institution conditions.