AIDS is the most serious public health problem in 21 century. The Department of Health of R.O.C. are becoming increasing concerned about HIV/AIDS prevention. Sex workers are recognized one of the main sources of transmit AIDS because their sex activities are very frequency and they are difficulted to choice their sex partners. So knowledge, attitude and perceived susceptibility of sex workers about HIV/AIDS are the important factors affected them to prevent is or rot. Total 31 young sex workers at a residential vocational training center for young women in Taipei were selected to this study. The young women at the center are transient, with low educational kevel and most return to prostitution upon leaving the center. Knowledge of HIV transmission, prevention and perceived susceptibility and condom use skill were the focus of this study. The results showed that knowledge of HIV transmission was high, selb-efficacy and perceived benefits of using condoms was low.