Background: Nutrition education is used as a way of promoting lifelong healthy eating practices among school adolescents. There is limited published information on the impact of nutrition education programmes in India. Objectives: To assess the knowledge and practices of high school students with respect to healthy diets before and after a nutrition education programme. Design: Pre- and post-intervention questionnaire survey. Setting: Two private schools in Chennai city. Method: This study was conducted among adolescents studying in standard VIII and IX in two private schools in Chennai city. Nutrition education as lectures and interactive discussions were given to students one hour every week for a period of 10 weeks. Information on knowledge and attitude on healthy eating and dietary practices was collected before and after the nutrition education intervention using a questionnaire. Differences in knowledge, attitude and practice of students on healthy diet were measured using the X2 test with the level of significance p<0.05. Results: A total of 181 students were involved in the study (response rate 92%). Following the nutrition education programme, satisfactory dietary knowledge significantly improved from 37% to 67% ( p<0.001). Similarly, students showing a positive attitude towards healthy diet increased from 18% to 40% ( p<0.001). The proportion of students taking soft drinks reduced from 20% to 10% ( p<0.01) and ingestion of fast food items through fast food restaurants reduced significantly. Conclusions: This short-term nutrition education programme brought significant improvements in dietary knowledge and reductions in soft drinks and fast foods consumption.