This study, through a correlational survey of 603 adolescent students in Onitsha Education Zone of Anambra State, Nigeria, aimed to find out if parental mediation is a moderator of the relationship between violent media contents exposure and aggressive behaviour. The researchers used Violent Media Contents Questionnaire and In-School Adolescents’ Aggressive Behaviour Questionnaire for data collection. To analyze the data collected, the researchers used Pearson product-moment correlation coefficient and simple linear regression statistics. Results showed that the extent to which parental mediation moderates the relationship between violent media contents exposure and aggressive behaviour among in-school adolescents was very high. It was also found that parental mediation significantly moderates the relationship between violent media contents exposure and aggressive behaviour among in-school adolescents. Therefore, parents could play an active role in managing and regulating in-school adolescent’s media contents consumption and invariably influence the extent they display aggressive behaviour.