Background: Use of mobile phones has both pros and cons but it has deleterious effect among students especially related to medical field. Objectives: to assess the effectiveness of structured teaching program on knowledge regarding hazards of using mobile phones among high school students in selected school at Bangalore, Karnataka, India. Methods: An evaluation research approach was used to assess the effectiveness of structured teaching program on knowledge regarding the hazards of using mobile phone among high school students in selected school in Bangalore. Statistics: Percentage was calculated for both pre-test and post-test. Results: Majority of students 19(63.3%) were in the age of 13-14 years. Most of the students 18(60%) were female. Majority of the students 16(53.3%) were Hindu. Most of them belongs to nuclear family 20(66.6%).Most of them have the family income of 14(46.6%) < 10,000.Most of them have total No. of siblings 17(56.5%).Most of them have monthly pocket money 27(90%) 100-200.Most of the students spend on mobile recharges 25(83.3%).Most of the students got information on hazards of using mobile phones through from friends 10(33.3%).Most of the students 18(60%) were not having any knowledge regarding side effects of mobile phones. The mean pre-test knowledge school scores were inadequate (70%). The mean post-test knowledge score was improved and it was found adequate (72%). Conclusion: There is significant difference between pre-test and post- test knowledge scores and it is evident that STP is significantly effective in improving knowledge regarding hazards of using mobile phones, high school students.