This study examined the level of Facebook use of 15-19-year-old teens in SouthEast Nigeria: the impact of parental mediation. It embodied four research objectives and four research questions. The study's theoretical frameworks were the theories of planned behaviour and parental mediation. Besides, the study adopted a survey as its research design. The research instruments were questionnaires and informant interviews. The sample size for the questionnaire-based or quantitative survey research design was 400, calculated using the Taro Yamane formula. Besides, the sample size for the interview-based or qualitative survey research design was 40, obtained using the Hagaman and Wutich data saturation method. The study presented and analysed its data using a 5-Likert scale, frequency table, simple percentage, and weighted mean scores. The findings showed that 15-19-year-old teens operated functional Facebook accounts. Hence, Facebook was popular among them. The findings also indicated that most teens started to use Facebook after thirteen years of age. Further, the findings revealed that most teens spent 30 minutes to two hours per Facebook visit. Likewise, the findings showed that most teens used Facebook multiple times daily. Besides, the findings indicated that parental mediation positively and negatively impacted 15-19-year-old teens. Subsequently, this study recommends, among others, media literacy to ensure optimal Facebook use among teens and their parents