The study examined students’ anti-social behaviours and their academic performance in public senior secondary schools in Port Harcourt Metropolis. To achieve the purpose of the study, the researcher formulated four (4) objectives, research questions and hypotheses to guide the study. The research design used is correlational research design. The population of the study consists of 12,000 students drawn from public senior secondary schools in Port Harcourt Metropolis. The sample size of the study was 387 students. The sample technique used was simple random sampling technique. The instrument used for data collection was self-structured questionnaire and Basic Education Certificate Result. The instrument was validated by the research supervisor and two other experts in Measurement and Evaluation, Faculty of Education. The internal consistency reliability through Cronbach Alpha was used to establish the reliability of the instruments which obtained a reliability coefficient of 0.88. The data were analysed using Pearson Product Moment Correlation Coefficient (PPMC) while the null hypotheses were tested using t-transformation at 0.05 level of significance. The findings of the study revealed that truancy, vandalism, rape and alcohol have negative relationship on students’ academic performance in public senior secondary schools in Port Harcourt Metropolis. However, the study recommends that Schools should have functioning counsellor; these counsellors should apply professional remedies at their disposal to treat anti-social behaviours of students. Parents should make their home suitable for child upbringing; the home environment includes the psychological aspects of happiness, love, care and morals. Teachers stand in loco parentis for these students and should provide them proper guidance. Appropriate sanction for breaking of rules should always apply. Parents, school heads and law enforcement agents are therefore enjoined to implement enabling laws.