Abstract: To probe.sex behavior characteristics and AIDS related knowledge attitudes and behaviors among drug users in Lanzhou city.Methods An anonymous investigation was carried out at adeto xification camp in Lanzhou city.Results 90.9% drug users had sex experience, 42.0% married drug users had ex tramarital sex, and 2.9 % drug users had homosexuality.57.1 % drug users were inhalers, 2.2% were injectors,and 10.8% of them took drug by both smoking and injection.29.5 % drug users took drug with regular people and 27.3% with irregular people.21.0 % injectors had used others syringes.Only 6.3% of them thought they might get AIDS virus infected.Only 41.7% of them thoug ht they would give up smoking when out of the detoxification camp.Co nclusions Because of the bad knowledg e, attitudes and behaviors on AIDS among drug users, Prev ention program should be canr red out urgently in Lanzhou city.