Previous research investigated the impact of psychosocial predictors (e.g. attitude, social and moral norm, perceived behavioral control, intention) on sustainable clothing purchasing. To date, no studies considered whether proenvironmental self-identity moderates the effects of these predictors on behavior. In this study, we adopted an intrapersonal approach and a longitudinal design to assess the moderating role of proenvironmental self-identity in predicting intentions and behaviors, considering gender differences. 250 participants completed an initial questionnaire on the predictors of three sustainable clothing purchasing. A month later, they filled out a second questionnaire to self-assess these behaviors. The results showed that social and internalized norms (moral norms) were notably influential of participants’ intentions. Affective attitude influenced behavior positively, while cognitive attitude had a negative influence. When considering the moderating role of proenvironmental self-identity, significant gender differences emerged. Women with a weak proenvironmental self-identity expressed a higher intention to purchase sustainable clothing when they had high affective attitudes and descriptive norm but low cognitive attitudes. Women with a strong proenvironmental self-identity intended to purchase sustainable clothing when they had high moral norms and cognitive attitudes but low descriptive norm. Man with a weak proenvironmental self-identity and high positive affective attitude increased their future SCP.