This survey research aimed to study the beliefs and patterns of sexual risk behavior of Thai adolescents and youths in education institutions in Songkhla Province. The sample included 1,156 adolescents and youths who were studying in secondary schools, vocational schools and universities from both public and private institutions. The data were obtained through both focus group discussions and in-depth interviews. A questionnaire about beliefs and patterns of sexual risk behavior was developed based on qualitative data analysis and literature review. Cronbach's alpha reliability of this questionnaire was 0.8. The results showed that belief on sexual relations among adolescents and youths of every educational level were similar. The common beliefs were that it is common for them to have sex with lovers (66.2%) or other acquaintance (48.6%) although they have had boy/girlfriend. They also felt that condom use increased sexual activities because they can prevent pregnancy. The overall mean age of first sexual intercourse was 15.9 years old, lower in males than in females. Only 29.9% of males and 35.2% of females had used a condom at their first sexual intercourse. There was a significant difference among males and females on whether it was acceptable to have sex, and in their understanding or ability to practice safe sex (p < 0.001).