Substantial research has explored the impact of peer stress on adolescents' deviant behaviors; however, the underlying mechanism remains underexplored. The current study investigated the longitudinal association between peer stress and deviant behaviors among Chinese adolescents, as well as explored the mediating effect of loneliness and moderating effect of stress mindset. Two-wave data were collected from 4,897 adolescents (Mage = 13.34, SD = 0.64; 50.6% girls) in Sichuan Province, China during the Autumn of 2023 (Time 1) and 2024 (Time 2). Adolescents completed a series of self-report measures of peer stress, stress mindset, loneliness, and deviant behaviors. After controlling for demographic covariates (i.e., age, gender, highest level of parental education, and subjective SES) and baseline loneliness, peer stress at Time 1 significantly predicted higher levels of deviant behaviors 1 year later. Additionally, peer stress exerted a significant indirect effect on deviant behaviors via increased loneliness at Time 2. Stress mindset moderated the direct association between peer stress and deviant behaviors. Specifically, the positive association between peer stress and deviant behaviors was significant for adolescents with a weaker stress-is-enhancing mindset, but was nonsignificant among those with a stronger stress-is-enhancing mindset. These findings shed light on the socioemotional pathway linking peer stress to deviant behaviors and highlight the protective effect of a stress-is-enhancing mindset. Interventions that decrease loneliness and promote more adaptive stress mindset may serve as practical and scalable approaches to mitigating deviant behaviors among adolescents.