Mental health is defined as the emotional, psychological and social well-being of human beings. In adolescents mental health is typically characterized by a roller coaster of emotional and psychological highs and lows. The most extensive usage of social media is correlated with numerous mental health issues, like anxiety of self-image, eating disorders and other problems which may influence the mental health of adolescent. Methodology: A descriptive study was conducted at Hacker Memorial Higher Secondary School, Neyyoor. Students between the age group of 15 - 18 years and studying in Hacker Memorial Higher Secondary School, Neyyoor were selected as samples by Convenience sampling technique. The test on usage of social media on behaviour pattern was conducted 30 minutes through demographic data and structured questionnaire. Results: Most of the sample subjects, 16 (53%) samples sometimes use social media, and 6 (20%) samples were very oftenly use social media.16 (53%) samples behavior was mildly affected, 6 (20%) samples behaviour was moderately affected. There is significant correlation between the social media usage and behaviour pattern score 0.14 which showed positive correlation between usage of social media on behaviour pattern. Conclusion:The study concluded that social media usage influence the behaviour pattern of adolescents.