Problematic patterns of gambling and their harms are known to have culturally specific expressions. For ethnic Chinese people, patterns of superstitious belief in this community appear to be linked to the elevated rates of gambling-related harms; however, little is known about the mediating psychological mechanisms. To address this issue, we surveyed 333 Chinese gamblers residing internationally and used a mediation analysis to explore how gambling-related cognitive biases, gambling frequency and variety of gambling forms (‘scope’) mediate the association between beliefs in luck and gambling problems. We found that cognitive biases and scope were significant mediators of this link but that the former is a stronger mediator than the latter. The mediating erroneous beliefs were not specific to any particular type of cognitive bias. These results suggest that Chinese beliefs in luck are expressed as gambling cognitive biases that increase the likelihood of gambling problems, and that biases that promote gambling (and its harms) are best understood within their socio-cultural context.