Background: Nurses treating patients having psychiatric disorders experience numerous stressful events affecting patients' care. Mindfulness mantram repetition, where a sacred word or phrase is silently repeated, can be used as a stress management technique to retrain an individual's attention. Aim: To evaluate the effect of mantram repetition as mindfulness strategy on psychological wellbeing among nurses in psychiatric wards. Design: Quasi-experimental (one group pre-post). Setting: The research carried out at "The Psychiatry, Neurology and Neurosurgery Center, affiliated to Tanta University Hospitals, Gharbya governorate, Egypt. Subject: A convenience sample of 50 nurses. Tools: two tools used in this research Tool I;The Perceived Stress Scale (PSS). Tool II; Ryff's Psychological Well-Being Scales (PWB). Results: A high statistically significant differences between nurses' levels of stress before and after the mindfulness mantram repetition intervention (P-value = 0.000). A high statistically significant differences between nurse's psychological wellbeing before and after the mindfulness mantram repetition intervention (P-value = 0.000), and a statistically significant negative correlation between nurses' level of stress, and their psychological wellbeing r = -.381, P-value = 0.06. Conclusion: The mindfulness mantram repetition intervention had a considerable positive impact on reducing the nurses' stress and improving their psychological wellbeing. Recommendations: Enhancing nurses' coping mechanisms by making time for mindfulness activities and encouraging them to use this activity.