IntroductionThe current study evaluated effects of an adapted version of Mindfulness-Based Relapse Prevention (MBRP) on several psychosocial indices in a sample of incarcerated adult males with substance use disorders. Method: This study used a 2 (baseline vs post-session) × 2 (MBRP vs. treatment-as-usual (TAU) mixed design. Twenty-four incarcerated individuals with a history of substance abuse were randomly assigned to either MBRP or TAU. At pre- and post-session assessment points, participants completed the Drug Use Identification Disorders Test- Extended (DUDIT-E), the Drug Avoidance Self-Efficacy Scale (DASE) and positive/negative outcome expectancies (Ep/En). The Beck Depression Inventory-II (BDI-II) was completed in each weekly session of MBRP. MANOVA and repeated measures ANOVA examined changes between and within subjects, with the significant level set at 0.05. Results No between-group differences were found on positive outcome expectancies or self-efficacy. Differences BDI-II scores among MBRP participants showed a downward trend over time. A Group × Time effect emerged for negative outcome expectancies, with significant differences between groups at post-course assessment. Conclusions Results from this randomized trial suggest pre- to post-intervention trend-level effects of MBRP on depression, and significant group differences over time and at post-course on negative outcome expectancies, with the MBRP group reporting increases