The cross-sectional descriptive study was conducted in Quat Lam and Thinh Long beach, Nam Oinh province, 2011 to assess the risks of behavior and some factors related to prevent HIV/AIOS among female sex workers (FSWs). Research results shows that 6.6 percent clients of FSWs need to have sex by mouth oranal. The rate of FSWs use condoms for the last having sex with new clients is 74.1 percent, with old clients is 54.1 percent and 73.9 percent with husband or boyfriends, 1.1 percent of FSWs had ever used drugs, 73 percent of FSWs had sexual transmisted infection, nearly 14 percent of FSWs had not correct answer about HIV transmission routes. Mainly factors related to not using condoms when having sex in FSWs: Low education, believed that their partner do not use drugs, more than 50 partners in each month, kind of work, listening about safe sex and safe injection drugs, knowledge in preventing HIV/AIDS.