This study aimed to examine the association between appearance comparison and adolescent depressive symptoms, the mediating role of body appreciation, and the moderating roles of gender and body-mass index (BMI) among adolescents in different age groups. A cross-sectional sample of 2645 Chinese students aged 12-16 years (44.7% girls) participated. The measurements included depressive symptoms, appearance comparison, body appreciation, weight, and height. Multigroup path analysis was used to examine the moderated mediation model. Compared with boys, adolescent girls presented greater levels of appearance, which increased with age. Body appreciation mediated the association between appearance comparison and depressive symptoms in girls, whereas appearance comparison directly correlated with depressive symptoms in boys. Body appreciation decreased with increasing BMI in boys but remained relatively stable in girls. Similar patterns were observed among junior and senior high school students. This study underscores the significant relationship between appearance comparison and adolescent depressive symptoms, suggesting varied mechanisms based on gender and BMI levels.