Purpose – The purpose of this research is to examine the impact of consumers’ levels of moral maturity on their unethical behavior. Design/methodology/approach – The research model of this study examines the effect of moral maturity on consumer ethics dimensions (“actively benefiting from an illegal situation” and “benefiting from actions perceived as harmless”). The universe of this descriptive research consists of consumers living in Turkey. The online survey method was applied to 457 consumers selected by convenience sampling method. While creating the questionnaire, moral maturity statements were prepared by using the scales developed by Sengun and Kaya (2007), and the consumer ethics statements were prepared by the help of the scale developed by Muncy and Vitell (1992). The results have been analyzed with SPSS and AMOS statistics programs. Frequency analysis, reliability analysis, explanatory factor analysis, confirmatory factor analysis and structural equation model analyses have been used. Findings – The findings suggest that the level of moral maturity has a significant and negative effect on both unethical consumer behavior dimensions: “actively benefiting from an illegal situation” and “benefiting from actions perceived as harmless”. Discussion – Moral maturity refers to the assimilation of moral principles, the evaluation of moral rules by the conscience, and the realization of actions in this direction. People who have reached the level of moral maturity are expected to display ethical behaviors in the society in daily life. According to the findings of the research, as the moral maturity of the individual increases, the possibility of exhibiting unethical behavior decreases; as the moral maturity decreases, the possibility of unethical behavior increases. The results obtained show how effective the concept of morality on ethical consumer behavior is. Marketing managers should consider the moral maturity of consumers in order to understand their unethical behaviors. In this direction, activities (such as training, seminars, public spots, education for children) can be carried out to increase the level of moral maturity of consumers. Besides this, marketing managers can prevent unethical consumer behaviors by applying different marketing strategies (in the conclusion section, the recommendations are mentioned in detail) to consumers with low/high moral maturity level.