Promoting environmentally conscious behaviour requires an understanding of the complex cognitive mechanisms by which people decide to act environmentally. Research suggests that locus of control (LOC), or the extent to which a person feels his or her own actions can produce broader change, is an important predictor of environmental behaviour; however, little is known about how LOC interacts with other cognitive motivators. This study uses a nationwide survey from China to test whether LOC moderates the effect of environmental attitudes on behaviour. Respondents with external LOC (i.e., those who believe personal actions cannot produce change) reported lower pro-environmental behaviour than those with internal LOC (i.e., those who believe personal actions can produce change). In addition, the influence of environmental attitudes on pro-environmental behaviour was stronger among respondents with external LOC than those with internal LOC. These results support efforts to promote conservation in China by promoting internal LOC and add a novel suggestion that attitude-based messaging is more efficacious among audiences with external LOC.