Background: According to World Economic Forum report 2011,  more than 60% of deaths worldwide are due to Non Communicable Diseases (NCDs), killing 36 million people each year.The beneficial role of physical activity in the prevention of NCD in adults has long been recognized. It is well established that health and development during adolescence in turn affect health during the adult years. Aims: To explore the patterns of physical activity and its determinants among school going adolescents. Methods & Materials: A school based descriptive survey conducted among 96 eligible adolescents selected using a multi-stage cluster sampling technique in Thrissur district, Kerala, with a structured pretested and validated questionnaire. Physical inactivity was defined as less than one hour of moderate and vigorous physical activity in a day. Results: The mean age of participants was 12.75±.92years. It was found that 57.3% don’t meet the requirements for 6 hrs of physical activity in a week 46.9% of children spent >2 hrs/day watching television. Physical activity was significantly associated with age and educational qualification of mother. Analysis was done using SPSS Version-16.Conclusion: Finding calls for an urgent need for population based strategies implemented at local and national level aimed at increasing levels of activity of adolescents to prevent escalation of non communicable diseases among young adults.