The present study examined the relation between changes in psychological flexibility and changes in mental health stigma in the context of a 2.5-hour long Acceptance and Commitment Therapy group workshop for reducing mental health stigma. Of 27 college undergraduates who attended the workshop, 22 completed one-month follow-up assessments, and their data were used for analyses. Results revealed that mental health stigma reduced significantly at post-treatment, and these reductions were maintained at one-month follow-up. The degree of improvement in psychological flexibility from pre to follow-up was found to be significantly correlated with the degree of reduction in mental health stigma from pre to follow-up. Limitations of the current study and directions for future research are discussed.