Street food and fast food are also taken in the same context as Junk. When we speak of street food, the fact that it’s cooked in unhealthy conditions makes it more unhealthy than the same food made at home. Coming to the latter, fast food is the kind of food item which can be made and served quickly. The biggest irony regarding junk food is the fact that it’s mostly prepared out of healthy food. Coming to Indian Junk food, locally called ‘Chaat’, these mostly include the Samosas, Kachoris, Panipuris/golgappas are fried items with various filling within an outer layer made of refined flour.In India, the consumer spending rate on processed food had increased at an average rate of 7.6% annually during the years 2008 to 2010 and this was expected to continue as the consumer expense would rise with an average of around 8.6% till the year 2012. 30% of children aged 2-19 years are considered overweight or obese and has been estimated that 1 in 3 children born in the year 2000 will develop diabetes in their lifetime over the past 3 decades the childhood obesity rate has more doubled for pre-school children aged 2-5 years and adolescents aged 12-19 years and it has more tripled for children aged 6-11 years.Thus the present study aimed at evaluating the effectiveness of structured teaching programme on ill effects of junk food among teenage students of Hilton Matriculation Higher Secondary School, Chrompet, Chennai-44. The purpose of the study is to assess the knowledge among teenage students before and after administering planned teaching programmeregarding ill effects of junk food, to assess the effectiveness of planned teaching program among teenage students regarding ill effects of junk food and to associate the post-test knowledge score with selected demographic variables ofteenage students. The study method was evaluative research approach and a pre experimental one group pre-test and post-test research design was used. Non Randomized sampling technique was used to select the sample. The total samplewas 40 teenage students. Pre- test and post-test scores was assessed by using standardized questionnaires. The result of the study concluded that mean and standard deviation of knowledge level score in pre-test was 6.3 and 2.31 and post test score was 10.4 and 2.98 the calculated ‘t’value was 11.4 which reveals that there was statistically highly significant difference between the pre-test and post-test score. It is evidenced that the planned teaching programme was significantly effective in improving knowledge regarding ill effects of junk food among teenage students.