The objective of this study is to find the most effective educational method on Sex and AIDS/HIV among young people in Korea. The number of people with HIV amounts to 1,224 as of Sep. 2000, and is increasing continuously, especially among young people(National Institute of Health, 2000). In setting up the policy of health education on Sex and AIDS, the criteria should be the effectiveness. By two-stage cluster sampling, 4,713 students were selected from among the 19,093 students from 44 middle and high schools and divided into three groups and taken the education with three different methods( 〈lecture with slides show〉, 〈lecture without any material〉 and 〈lecture through broadcasting system〉) by the same lecturer with the same contents for about 50 minutes. To compare the effects of education by methods, the tests on the AIDS knowledge, AIDS attitude on AIDS and Sexuality attitudes with self-administered questionnaire were implemented three times, that is, ‘before’, ‘right after’ and ‘2 weeks later’ of the education. As to the degrees of change of AIDS knowledge, AIDS attitudes, Sexuality attitudes and subjective evaluation of the education, 〈lecture with slides show〉 was the most effective, 〈lecture without any material〉 was the second and 〈lecture through broadcasting system〉 was the least effective, respectively. In the cost-effectiveness analysis using the results of this study, 〈lecture with slides show〉 turned out to be the most effective, and 〈lecture through broadcasting system〉 was the second and 〈lecture without any material〉 was least effective. From these results, it is suggested that 〈lecture with slides show〉 is more effective health educational methods on Sex and AIDS than 〈lecture without any material〉 or 〈lecture through broadcasting system〉.