Extant literature has reported mixed findings on the effectiveness of praising versus scolding in social marketing messages, such as how to encourage consumer engagement with plastic waste issue. Against this backdrop, this research investigates the moderating role of consumers' mindset in this regard. This research reports two experimental studies and demonstrates that consumers with a growth (vs. fixed) mindset will experience higher levels of outcome efficacy when evaluating a scolding (vs. praising) message. In addition, this research employs different methods of eliciting consumers' mindset and examines different dependent variables (product choice in Study 1 and donation allocations in Study 2). The results of this research thus offer a fresh theoretical perspective on the effectiveness of scolding (vs. praising) in enhancing consumer engagement with plastic waste issue by examining the moderating role of consumers’ mindset and establishing the underlying mechanism.