This paper investigates the impacts of competition structures on firms’ incentives for adopting strategic environmental corporate social responsibility (ECSR) certified by a Non-Governmental Organization. We show that, to induce firms to adopt certified ECSR, the certifier will set a standard lower than the optimal one, and the standard in Cournot competition is higher than that in Bertrand competition. Finally, we show that firms and consumers benefit from firms’ certified ECSR. •Effects of competition modes on a NGO certifier’s standard setting are examined.•Effects of certification on firms’ strategic incentives for ECSR are also examined.•The NGO certifier will set a standard lower than the optimal one.•The standard in Cournot competition is higher than that in Bertrand competition.•Firms and consumers both benefit from firms’ certified ECSR.