Background: Food insecurity, a pervasive global issue exacerbated by the COVID-19 pandemic, has been linked to adverse mental health outcomes. However, the role of social capital in mitigating this relationship remains understudied, particularly in the Chinese context. Aims: This study investigated the associations between food insecurity and psychological distress (depressive and anxiety symptoms) and examined the potential moderating effects of bonding and bridging social capital among Chinese adults in Shanghai. Methods: This cross-sectional study included 3,220 Chinese adults (mean age: 34.45; 51.5% male) in Shanghai. Food insecurity was assessed using the modified Household Food Insecurity Access Scale, psychological distress was measured using the Patient Health Questionnaire-9 and the Generalized Anxiety Disorder-7, and social capital was evaluated using the Revised Personal Social Capital Scale. Results: Multivariable linear regression analyses revealed that food insecurity was significantly positively associated with both depressive (β = 0.449, SE = 0.024) and anxiety symptoms (β = 0.391, SE = 0.022), after adjusting for sociodemographic characteristics, health status, and COVID-19-related factors. Higher levels of bonding and bridging social capital were significantly associated with fewer depressive and anxiety symptoms. Significant interactions ( p < .001) between bonding social capital and food insecurity indicated that the associations between food insecurity and psychological distress were less pronounced among adults with higher bonding social capital. Conclusions: These findings highlight the critical role of food insecurity as a risk factor for psychological distress and the importance of bonding social capital in mitigating its impact on mental health. Policies and interventions targeting food insecurity prevention and bonding social capital enhancement may promote better mental health outcomes among Chinese adults.