In Vietnam, the public sector has largely been responsible for delivering methadone maintenance treatment (MMT) services. However, with foreign aid anticipated to decline in the coming years, the involvement of the private sector in delivering MMT services is critical to ensure the continued sustainability of MMT programs across Vietnam. This study aims to evaluate patient satisfaction and identify correlated factors among Vietnamese drug users undergoing MMT in both public and private methadone clinics. A cross-sectional study was conducted in one private and two public methadone facilities in Nam Dinh, a province in the North of Vietnam. A convenience sampling technique was applied to recruit 395 participants. Data was collected through 20-minute face-to-face interviews using a structured questionnaire. Multivariate Tobit regression was utilized to measure associated factors with patient satisfaction. Results showed that patients were highly satisfied with MMT services in both public and private; however, they expected a higher degree of comprehensive care services. Compared with public facilities, the satisfaction level of patients in private facilities was significantly lower in the following aspects: health administration and professional capacity of health workers. However, there were insignificant differences in regard to infrastructure, equipment, and availability of medical services resources, supporting a promising role of the private sector in supporting the expansion of the MMT programs in Vietnam. Integrating MMT with other physical and mental healthcare services, along with strategies for improving administrative procedures and health workers' capacity in private clinics, are critical implications of this study.