Objectives: Research in recent years has shown that mindfulness-based interventions can enhance teachers’ mental and physical health. However, the existing studies were predominantly conducted in Western, educated, industrialized, rich, and democratic (WEIRD) societies. As a randomized controlled trial in a non-WEIRD society, the present study examined the effectiveness and mechanisms of mindfulness training for Hong Kong teachers in difficult times. Methods: Teachers from primary and secondary schools (n = 186) were randomly assigned to mindfulness training (eight-week .b Foundations) or waitlist control condition. They completed online self-report surveys on measures of well-being, emotion management, and mindfulness in teaching at baseline, post-intervention, and two-month follow-up. Results: The intervention group reported significantly higher levels of life satisfaction, positive affect, general health, along with significantly lower levels of insomnia, stress, and negative affect than the control group at post-test and two-month follow-up. The effect sizes were medium to large (ηp2 = 0.06 to 0.14). More importantly, teachers’ baseline well-being had a significant moderating effect on the intervention effectiveness. Those with a lower baseline in well-being benefitted more than their counterparts with a higher baseline. In addition, teachers’ emotion management was found to be the mediator through which mindfulness training enhanced teachers’ well-being. Such improvement in well-being also predicted higher levels of mindfulness in teaching. Conclusions: This study provides evidence on the efficacy of mindfulness training for teachers beyond WEIRD societies. It suggests the universality and practicality of mindfulness training in enhancing teachers’ well-being and reducing their distress in difficult times. Copyright © 2021 The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.