Objective This study was conducted to evaluate the effectiveness of a brief mindfulness-based training program in reducing stress and promoting well-being among critical care nurses. Design A quasi-experimental, single-group, pre-post study design was used to evaluate the effectiveness of the program. Setting This study was conducted in a tertiary referral centre in Malaysia. Subjects A non–probability voluntary sample of 41 critical care nurses participated in the program. Thirty seven (90%) completed the program, with at least 80% attendance. Intervention The intervention is an adapted and brief version of Mindfulness-based Cognitive Therapy (b-MBCT) using the local promotional name of ‘Mindful-Gym’. b-MBCT is a group-based program, carried out for five weeks at two hours per week with practice sessions in between. It was delivered as part of the hospital’s continuing nursing education program. Main outcome measures Perceived Stress Scale (PSS) and Depression Anxiety Stress Scale (DASS) were used to measure the stressrelated outcomes. As for the well-being outcomes, the Mindfulness Attention and Awareness Scale and Subjective Happiness Scale (SHS) were used.Results fter completing the program, the participants reported significant improvement in the level of perceived stress (PSS: p < .001; r = 0.50), stress (DASS-S: p = .002; d = 0.56), anxiety (DASS-A: p < .001; r =0.38), depression (DASS-D: p < .001; r = 0.37), mindfulness (MAAS: p < .001; d = 1.002), and happiness (SHS: p = .028; d = 0.57), with a moderate to large effect size. Conclusion Results support the effectiveness of b-MBCT in reducing stress and promoting well-being among critical care nurses.