Although methadone maintenance treatment (MMT) is an important means of HIV control, MMT clinics commonly have high attrition rates. The randomized controlled trial investigated the relative efficacy of adding a psycho-social intervention to the standard-of-care MMT in reducing attrition and non-attendance among first-time newly admitted MMT users in China (n = 288). Social workers implemented this three-phase intervention that was based on a behavioral maintenance theory. It also involved participants' family members and rectified some MMT-related misconceptions. As compared to the control group, the intervention group showed significantly lower likelihood of attrition (HR = 0.55, 95% confidence interval 0.39-0.80), lower estimated probability of attrition at Month 12 (0.35 vs. 0.55), and higher median number of days of attendance (Month 6: 147 vs. 91 days, p < 0.001; end-date: 225 vs. 142 days, p < 0.001). Further psycho-social services and translational research are warranted.