Social media addiction (SMA) is considered a risk factor for aggressive behaviors in adolescents, while its underlying mechanisms remains unclear. In this study, we investigated the possible mediating roles of nighttime social media use and sleep quality in the relationship between SMA and aggressive behaviors. A sample of 773 Italian secondary school students (49.9% female, age range = 11-15 years) completed a self-report questionnaire that included information on SMA, nighttime social media use, sleep quality, and aggressive behaviors. Results indicated that SMA was positively associated with aggressive behaviors. In addition, SMA was positively related to nighttime social media use and negatively related to sleep quality. Nighttime social media use was associated with a poorer sleep quality, which in turn associated with more aggressive behaviors. Analyses indicated that both nighttime social media use and sleep quality were mediators in the relationship between SMA and aggressive behaviors in adolescents.