Abstract: Objective To understand the influencing factors for anti HCV positive seroconversion in drug users in methadone maintenance treatment (MMT) clinic in Baoshan, Yunan province. Methods Questionnaire survey and serological detection were carried out in the drug users who had HCV detection record and their latest record of HCV were negative in MMT clinic in Baoshan in July 2015. Meanwhile, 5 ml venous blood were taken for HCV antibody detection. Database was established by using software EpiData 3.0, and the data were analyzed with software SPSS 19.0. Results The cumulative anti HCV positive seroconversion rate was 17.00% (34/200), the person year incidence density was 30.36% (34/112). The awareness rate of their anti HCV positive seroconversion and non-positive seroconversion was 70.59% (24/34) and 52.40% (87/166) respectively, there was no significant difference (P0.05). Non conditional logistic regression analysis showed that injection drug use (IDU) (OR=1.807, 95%CI: 1.000-2.460, P=0.001) and addicted to alcohol (OR=2.749, 95% CI: 1.181-6.398, P=0.019) were the risk factor for anti HCV positive seroconversion. Conclusion The anti HCV positive seroconversion of drug users in MMT in Baoshan was high and rapid, and it is necessary to strengthen the health education and behavior intervention in drug users, including injection drug users and alcohol dependent drug users.