Abstract： Objective To investigate the proportion of methadone maintenance treatment(MMT)clients continuing to use heroin and to explore its associated risk factors.Methods All 1003 heroin addictive patients were recruited from eight MMT clinics in Guizhou province and followed up for 14 months.During the 14 months,each MMT client received random urine tests.MMT clinics,gender,marital status,employment,ethnicity,religion,previous drug using method,having a history being in detoxification program,age,methadone dosage,education level and length of drug use were treated as potential predicting variables into the GEE model.Results The average age of the 1003 clients was(33.3±6.1)years old,the average length of drug use was(8.0±4.0)years,and the average daily methadone dosage was(38.0±16.6)mg.Among the 1003 clients,26.0%were female drug users,15.5%were divorced and 35.8%had a full time job.The rate of positive urine samples was approximately 30%for the first 10 months of follow-up,after which the positive rate decreased.The model found that different MMT clinics,the average daily methadone dosage(RR=0.98,P=0.003),treatment duration(RR=0.95,P=0.029)and years of education(RR=0.94,P=0.014)were associated with patients positive urine teat. Conclusion Continued heroin use was common in MMT clinics in Guizhou province:increasing the dosage of methadone and the duration in the treatment program might decrease the continued use of heroin among clients in MMT clinics.