--- - |2+ Abstract Background Studies have found lower well‐being among prisoners than in the general population. Positive psychological interventions provide fruitful ways of enhancing people's well‐being, but little is known about whether these contribute to prisoners' well‐being. Aims To test the effects of two typical positive psychological interventions – kindness and gratitude – on Chinese prisoners' well‐being. Methods One hundred and forty‐four participants were randomly assigned to three conditions: kindness or gratitude groups in addition to ‘treatment as usual’ and a control condition of treatment as usual alone, with 48 men in each condition. Participants completed established well‐being measures before and after the 6‐week intervention and a similar period in control conditions. Results Both kindness and gratitude interventions significantly increased prisoners' well‐being compared to the control group. The kindness intervention promoted higher well‐being than the gratitude intervention. Conclusions Although both kindness and gratitude interventions enhanced prisoners' happiness and mitigated negative affect, the weaker effect of the gratitude condition reflects Chinese strongly communal culture, so further cross‐cultural studies would be of interest. Future research should also include longer term follow‐up and expand the work to include women in prison. - 'Criminal Behaviour and Mental Health, Volume 28, Issue 5, Page 433-441, October 2018. '