Purpose: There is a perception that non-religious consumers are less ethical than religious consumers. Studies found prejudices against atheists around the world and assumed that those who committed unethical behavior were more likely to be atheists. Hence, first, the purpose of this study is to investigate the effect of consumers’ intrinsic religiosity, extrinsic religiosity and atheism on consumers’ ethical beliefs. Second, this study attempts to segment consumers and identify differences between these segments. Design/methodology/approach: Using data from 235 study participants in the USA and 531 in Vietnam. Subsequently, a two-step cluster approach was used to identify segments within these samples. Findings: The study results show consumers’ intrinsic religiosity negatively influences all consumers’ unethical beliefs. Similarly, atheism also negatively influences all consumers’ unethical beliefs. This study also complements other studies exploring consumer ethics in developing countries. In addition, the segmentation analysis produced unique segments. The results from both samples (USA and Vietnam) indicated that non-religious consumers are less likely to accept various unethical behaviors compared to religious consumers. Religious consumers are not necessarily more ethical and atheism consumers are not necessarily less ethical. In the end, are implications for business ethics, religious and non-religious leaders on how to view the impact of beliefs on consumer ethical behaviors. Originality/value: This is one of the first few studies investigating the impact of atheism on consumer ethics. The results of this study further extend the knowledge of study in consumer ethics by comparing consumers’ religiosity and atheism.