Abstract: Objective To investigate the addiction severity of drug dependent patients with methadone maintenance therapy and its influential factors.Methods Totally 462 heroin dependent patients receiving methadone maintenance therapy in Dehong prefecture,Yunnan province were randomly selected with proportionally stratified sampling and interview ed with the measurement instrument of addiction severity index to measure their addiction severity in past one month and lifetime,and the influential factors related to addiction severity.Results Among the 462 patients,451 patients(97.6%)were male and 270 patients(58.44%)were married,with an average age of 37.80±9.13 years.The patients had a score of 1.02±0.42 for total addiction severity and and scores of 0.11±0.18,0.47±0.15,0.09±0.07, 0.08±0.13,0.01±0.03,0.23±0.14,and 0.05±0.11 for the seven functional domains of medical health,employment/self support,drug use,alcohol use,illegal activity,family relation,and psychiatric health,respectively.The addiction severity for the patients with different w ays of drug use was different in medical health,alcohol use,illegal activity,and family relations before receiving the treatment(F=5.450,P=0.001).The addiction severity for family/social relations of the patients with first use of drug at the age of younger than 16 years was significantly higher(P<0.05).The adition severity for drug use and alcohol abuse was different among patients with the drug use years of less than 5,5-10,and longer than 10 years before methadone maintenance therapy.Conclusion Addiction severity of heroin dependent patients adhering to methadone maintenance therapy could be decreased.