Background: Relapse and treatment dropout are key challenges in opioid use disorder that need effective intervention strategies. Motivation enhancement therapy may be effective in improving opioid use disorder treatment outcomes. Objective: To assess the effectiveness of group motivational enhancement therapy (GMET) in patients with opioid dependence. Methods: It is an open-label, two-arm, parallel-group, randomized controlled trial (RCT). Participants include patients with opioid dependence and on opioid maintenance treatment, aged between 18 and 60 years. The intervention consists of six GMET sessions, each lasting about 45 minutes. Assessments will be conducted at four time points—baseline, six weeks, four months, and six months—using the Kessler psychological distress scale (K10), Recovery and Relapse Prevention Inventory Diagnostic (RAPID), WHO Quality of Life-BREF, Harm Reduction Self-Efficacy Questionnaire and Stage of Change Readiness and Treatment Eagerness Scale for drugs (SOCRATES 8D). Conclusion: The customized GMET approach tailored to the specific needs of the local population is expected to enhance the effectiveness and feasibility of the intervention and its implementation.