Online community administrators are attempting to encourage their users to contribute knowledge and resources in order to provide value to members and ensure sustainability. A large number of online communities fail mainly due to the reluctance of users to share knowledge in them. Many studies on this topic have highlighted the importance of reciprocity for knowledge contribution. However, it is unclear how reciprocity is developed and what influences its development. Motivated by this concern, this study focuses on investigating the antecedents of knowledge receivers’ reciprocity in online communities. It formulates and tests a theoretical model to explain reciprocity behaviour of knowledge receivers based on equity theory and Social Identity explanation of De-individuation Effects (SIDE) model. Our proposed model is validated through a large-scale survey in an online forum for English language learning. The results reveal that indebtedness and community norm not only are key antecedents of intention to reciprocate but are also positively related to each other. The perceived anonymity of the online community not only has a positive effect on indebtedness and intention to reciprocate, but also has an interactive effect with community norm on intention to reciprocate. Theoretical and practical implications of this study are discussed.