Abstract: Objective The present investigation was performed to evaluate AIDS and syphilis infection in drag abusers and their knowledge and behaviors related to the diseases in Zhongshan city Methods From 1999 to 2003，11759 drug abusers of the city were tested for HIV and syphilis antibodies，with Iace-to-face Interview conducted for 2047 of them to understand the rate of their awareness of related knowledge and their high-risk behaviors Results 574 cases were found to be positive for anti-HIV an tibody (4.88％)：683 cases positive for syphilis antibody (5.81％)：and 16 cases positive for both HIV and syphilis antibodies (0.14％) Those having AIDS-related knowledge accounted for 48.27％ 79.04％. 55.30％ of the investigated were intravenous drug-abusers，with the rate of needle sharing being 58.07％. 18.20％ of the interviewed had non-marital sexual contacts half a year before detained 51.47％ used a condom in the last sexnal rdation 48.53％ reported no condom use Condllsion HIV and syphilis infections among drug-abusing population are relativdy low，but have a high risk of potential prevalence Paricular precautions have to be taken to prevent transmission of HIV and syphilis from drug abusers to unlicensed prostitutes or whoremaster and to family members Comprehensive interven-tions need to be reinforced further