Drawing on the theory of responsible environmental behaviour, the study seeks to examine the relationship between internal environmental locus of control (IntLOC)and behaviour towards sustainable apparel in the presence of intention to purchase as a mediator. Consumer knowledge about sustainable apparel was applied as a moderator in this mediated relationship. Data was collected from a sample of 294 Gen Z consumers through an online questionnaire Structural Equation modelling and Hayes PROCESS MACROS were the statistical tools employed to test the moderated mediation model. The results depict that IntLOC is animportant predictor of purchase behaviour towards sustainable apparel products. Intention to purchase has also been established as a partial mediator in the mode. Finally, consumer knowledge also acts as a significant moderator in the study.