Abstract: Objective To examine characteristics of acquired immunodeficiency syndrome(AIDS)-related knowledge and behaviors among common and new illicit drug users.Methods A face-to-face questionnaire survey and detections for serum antibody of human immunodeficiency virus(HIV),Treponema pallidum(TP),and hepatitis C virus(HCV)were conducted among 3 844 new attendees recruited from several drug rehabilitation centers in Inner Mongolia Autonomous Region during 2015.Differences in the knowledge and behaviors were compared between the abusers of common and new illicit drugs.Results There were significant differences in demographic characteristics including age,gender,marital status,education level,and registered residence between the abusers of common and new illicit drug (P < 0.05),except for in nationality.The ratio of injection drug use was lower among the new illicit drug users than among common illicit drug users (13.3% vs.35.3%,P < 0.001).Compared to the common illicit drug users,the new illicit drug users reported a significant higher ratio of commercial sex behavior and a lower ratio of condom use in sexual behavior (both P < 0.05).There were statistically significant differences in AIDS-related knowledge and utilization of intervention services between the two groups (P < 0.05 for all).The positive rate of serum TP antibody in the new illicit drug users was significantly higher than that in common illicit drug users (χ²=43.06,P < 0.001).Conclusion New illicit drug use is a high risk factor for the transmission of AIDS.