This study explores the role of teachers’ social support in students’ emotional and cognitive presences in online learning. Two-hundred and seventy-one Chinese university students were surveyed with an online questionnaire on their perceived social support, emotional presence, and cognitive presence. Partial least squares structural equation modeling (PLS-SEM) was employed to analyze the role of teachers’ social support in students’ emotional and cognitive presences. Results demonstrate that the two indicators of teachers’ social support (i.e., emotional support and reflective support) accounted for 59.2% of students’ emotional presence and 78.2% of cognitive presence. Specifically, reflective support demonstrated significant positive correlations with emotional and cognitive presences. Teachers’ emotional support demonstrated a positive correlation with emotional presence. Additionally, emotional presence had significantly positive correlations with cognitive presence. Results indicate that reflective and emotional support play essential roles in students’ online learning.