This research was designed to investigate the homosexual behavior, some factors related to homosexual behavior, and attitude toward homosexual behavior of adolescent students in Educational Region 6 of Thailand. The research sample was 953 adolescent students who were studying in high school and vocational school during the second semester of acadamic year B.E.2531. The research questionair was designed to measure homsexual behavior and attitude toware homosexual behavior. The frequency distribution, percentage, Chi-square test, t-test and analysis of variance were used to examine the result of the study. The results indicated that the percentage of adolescent students who had homosexual behavior were 3.3,1.2 were male and 2.1 were female. The percentage of adolescent students who had high risk of homosexual tendency were 19.9,9.0 were male and 10.9 were female. The proportion of homosexuality between male and female had no significant difference The students in girl school had more homosexual behavior than boy and co-educational school which were equal. In male, there were significantly proportion of homosexual behavior in boy school than in co-educational school.But in female, there was no siginificant difference. Regarding to the family factors, the study showed that father and mothers expression which were non-love or love toward sons more than daughters, sibling relationship were not helpful and familiarity with homosexual related with developing homosexual behavior in girls and mother-child relationship which were overprotection related with developing homosexual behavior in boys. The atitude of male students on homosexual behavior was better than female studenst. According to the different types of school factor, ineach sex group , the study found that male and female students who stdy in boy and girl school had better attitude than male and female students who study in co-educational school. Students who had homosexual and non-homosexual behaviors thought that causes of homosexuality were missing associate with opposit sex experience, imitating between adolescence and satisfied homosexual experience. And mass media showed matter about homosexuality were general newspapers, movies and televisions. The study showed rather high proportion of homosexual behavior students and high risk of homosexual behaviors among students studied and there was a relation of family factars and homosexual behavior among adolescent students. It was recommended that parents, guardians, teachers and those involved in the development of adolescence consider serious effort to prevent homosexual behavior among adolescence.