This study enhanced nutritional knowledge in an education program and encouraged healthy dietary habits and regular physical activity among teenagers. A total of 203 adolescents from a secondary school in Hong Kong took part in the study. Their Body Mass Index, dietary habits, and physical exercise pattern were recorded and examined before and after the health education program. The prevalence of overweight and obesity, together with the fat composition, were high among the participants before the nutrition education program. There was a marked gain in knowledge upon its completion. A follow-up action conducted 3 months later revealed positive outcomes in relation to the diet and physical activity level. The teenagers were able to take control of their health and requested the tuck shop to sell more healthy food and reduce the supply of unhealthy items. The educational initiatives in dietary habits and physical activities proved to be effective in encouraging the teenagers to eat more healthily and to adopt an active lifestyle.