The study was to describe knowledge and attitudes towards sexual transmitted diseases, HIV/AIDS among adolescents in Phu Luong, Thai Nguyen in 2009. Cross-sectional descriptive study, interviewed 398 adolescents. The results showed that sex is not safe to transmit HIV/AIDS was best known (91 percent among men and 97 percent among women). HIV transmission from mother to child was known lower. The rate that would not use condoms during sexual intercourse was higher among men than that among women (6.8 percent versus 2.5 percent). A quite relative percentage of adolescents did not sure using a condom during sex (20.4 percent for men and 13.6 percent for women, p 0.05). Intervention activities to improve knowledge on sexually transmitted diseases, HIV / AIDS for adolescents are essential.