Aggression in adolescents is a complex issue involving verbal hostility and physical brutality. It can be harmful for both the perpetrator and victim, and can ruin an adolescent's future. Adolescents often struggle with adjustment to changes in their physical and mental well-being, which can be influenced by factors like substance abuse, sexual experimentation, and strained relationships. Gaming addiction has also been linked to the development of aggressive behaviors among adolescents. This study aimed to assess effectiveness of structured intervention module on aggression among adolescents. A true experimental study was conducted among 348 adolescents each from control, and experimental group. The questionnaire was developed by using Aggression Scale. Data were coded, entered and analysed with the help of Software Statistical Package for Social Sciences (SPSS) version 21. Data analysis were done by using descriptive (mean, frequency, percentage and standard deviation) and inferential (paired t-test) statistics to find out the relationship. The control group consisted of 56.3% male participants aged 16-17 years, while the experimental group had 79.9% male participants aged 18-19 years. The majority of participants belonged to the Janajati ethnic group, with 44.4% belonging to this group and 37.1% belonging to the experimental group. After the intervention, there was a significant decrease in the level of aggression among the experimental group, dropping from 69.0% to 56% at the end of the 3-week post-intervention period and further reducing to 38.5% at the end of the 6-week post-intervention period. During the post-test at 3 week, there was a significant difference in mean scores for aggression between the control group (37.8±14.7) and experimental group (22.0±18.0) and similarly at 6 weeks post-test between control group (37.7±14.6) and experimental group (11.1±0.7) with a p-value of less than 0.0001. The study showed that structured intervention module was effective in reducing aggression among adolescents in experimental group. Conducting similar school based educational interventions among adolescents can help to prevent and reduce aggression.