OBJECTIVE: To examine the effectiveness of group mindfulness-based intervention (MBI) in patients diagnosed with severe mental illness. The primary outcome was health-related psychological quality of life. Secondary measures were environmental, social and physical health related quality of life, frequency and intensity of psychotic symptoms and daily-life mindfulness. METHOD: Forty-four patients from a public community rehabilitation center for people with severe mental illness were recruited, and randomly allocated to Integrated Rehabilitation Treatment (IRT) or IRT plus MBI. Measures included PANSS interview, WHOQOL-BREF, and Mindfulness Attention Awareness Scale. MBI comprised 26 one-hour weekly sessions. Intention-to-treat analysis was used. RESULTS: One patient did not complete IRT+MBI and two did not complete IRT. At baseline there were no statistical group differences in demographic characteristics or primary and secondary outcomes. At post-treatment interaction between treatment and time in health-related psychological quality of life was statistically significant, and simple effect analysis showed significant differences for between and within subject factor in favor of MBI. Interaction was also significant in PANSS negative symptoms, simple effects showed a statistical trend in within subject factor. Time factor was significant in environmental and physical quality of life. CONCLUSIONS: Data suggest mindfulness added to IRT may enhance psychological quality of life in people with severe mental illness from a public community center. Results also suggest that mindfulness may impact frequency and intensity of negative symptoms.