Academic stress is a commonly reported affective state by high school students that can be accompanied by unwanted and unhelpful short-and long-term implications including a low sense of school belonging. Understanding how academic stress may be alleviated or managed by students is an essential consideration for all schools concerned with student well-being. This study aimed to examine the relationship between academic stress and sense of school belonging, as well as the mediation effect of academic hardiness. Four hundred and five high school students from six schools in Tehran (Iran) were recruited in the study. Data analyses with Structural Equation Modeling revealed that a sense of belonging to school ([beta] = -0.38, p < 0.01) and academic hardiness ([beta]= -0.40, p < 0.01) were significant predictors of academic stress. Bootstrapping analysis showed that academic hardiness acted as a mediator between a sense of belonging to school and academic stress. The findings elucidate the underlying mechanism in how low school belonging may lead to academic stress in high school students. Creating a culture of school belonging and teaching and supporting skills related to academic hardiness should be key considerations for all schools seeking to reduce academic stress experienced by their students.