<p>Social context is an important factor in determining individual socioemotional development. Whereas unsociability is often perceived as a negative behavior in Chinese adolescents, little is known about how classroom environment plays a role in shaping the adjustment outcomes of unsociability. To address this gap, this study examined the moderating effects of classroom cultural norms on the longitudinal relations between unsociability and later school and psychological adjustment in Chinese young adolescents. Participants included 2,693 students (1,348 boys, <i>M</i> age = 13.24 years, <i>SD</i> = 0.56 years) at the 7th grade in middle schools in a region consisting mostly of towns, small cities, and surrounding rural areas in East China. Data on individualistic and collectivistic cultural orientations, unsociability, peer preference, and adjustment were obtained from multiple sources including peer nominations, teacher ratings, and self-reports. The class cultural norms were calculated by correlating the individual cultural orientations and peer preference score. The results show that unsociability was negatively associated with later school competence and positively related to later psychological problems in classrooms with a weak individualistic norm or a strong collectivistic norm. The associations were not significant in classrooms high on individualistic norm or low on collectivistic norm. The results indicate that weak individualistic norms or strong collectivistic norms in the classroom may exacerbate adjustment problems of unsociable adolescents in China.</p>