the aim of present study was to investigate the mediating roles of self-system processes, academic motivation and emotions in the relationship between classroom social context and academic engagement. The participants were 586 grade nine students in Tehran. They completed Academic Engagement Questionnaire (Reeve & Tseng, 2011), Academic Emotions Questionnaires (Pekrun et al., 2005), Academic Motivation Scale (Vallerand et al, 1989), Psychological Needs Satisfaction Scale (Filak & Sheldon, 2003), Teacher Emotional Support Scale (Sakiz, 2007), Autonomy Support (Blackburn, 1998) and Peers Emotional Support (Johnson et al, 1983) subscales. The results of path analysis showed that classroom social context (including teacher emotional support, autonomy support and peers emotional support) have effects on academic engagement through several pathways. Findings indicated that social context factors of classroom had effects on self-system processes (autonomy need satisfaction, competence need satisfaction and relatedness need satisfaction), and these processes influenced academic motivation. Academic motivation had an effect on academic emotions, and academic emotions structurally influenced academic engagement. Therefore, classroom social context had effects on academic engagement by the mediating roles of self-system processes, academic motivation and emotions.