Adolescents with HIV (AWH) face the double burden of dealing with challenges presented by their developmental phase while coping with stigma related to HIV, affecting their mental health. Poor mental health complicates adherence to daily treatment regimens, requiring innovative psychosocial support strategies for use with adolescents. We assessed the effectiveness of a mindfulness and acceptance-based intervention on the mental health of AWH in Uganda. One hundred and twenty-two AWH, mean age 17 ±1.59 (range 15 to 19 years), 57% female, receiving care at a public health facility in Kampala were enrolled in an open-label randomized trial (ClinicalTrials.gov: NCT05010317) with assessments at pre-and post-intervention. The mindfulness and acceptance-based intervention involved weekly 90-minute group sessions for four consecutive weeks facilitated by two experienced trainers. Sessions involved clarifying values, skillfully relating to thoughts, allowing and becoming aware of experiences non-judgmentally, and exploring life through trial and error. The control group received the current standard of care. Three mental health domains (depression, anxiety, and internalized stigma) were compared between the intervention and control groups. A linear mixed effects regression was used to analyze the effect of the intervention across the two time points. Results showed that the intervention was associated with a statistically significant reduction in symptoms of depression (β = -10.72, 95%CI: 6.25, -15.20; p < .0001), anxiety (β = -7.55, 95%CI: 2.66, -12.43; p = .0003) and stigma (β = -1.40, 95%CI: 0.66 to -2.15; p = .0004) over time. Results suggest that mindfulness and acceptance-based interventions have the potential to improve the mental health of AWH.