Objective: This randomized controlled trial examined whether KORSA workshops indirectly influence anxiety, depression and stress symptoms among university students through their effect on two second-order psychological flexibility processes--(1) mindfulness and acceptance, and (2) commitment and behavior change. Participants: During the fall 2014 and the winter 2015 semesters, 124 students participated in the study. Methods: They were randomized to either a 4-week intervention group (n = 61) or a wait-list control group (n = 63). They completed measures of anxiety, depression, stress and psychological flexibility before and immediately after the intervention. Results: Bootstrapping-based mediation analyses showed that the intervention indirectly influenced symptoms reduction through its effect on acceptance and mindfulness processes, but not through commitment and behavior change processes. Conclusions: These initial findings suggest that contact with the present moment, acceptance, cognitive defusion and self as context are important processes of change through which KORSA workshops affect the students mental health.