University students are at risk for depression, considering the processes of change they are going through. Depressive symptoms of students may increase during the stages of adaptation to the pandemic and its subsequent processes. The first important indicator of depression is rumination. Rumination causes departure from psychological flexibility, which is an important component in protecting mental health. On the other hand, cognitive defusion enables one to distance oneself from repetitive negative thoughts. Considering that cognitive defusion is a mediating variable in coping with rumination and increasing acceptance and psychological flexibility, the study aims to examine the mediating role of cognitive defusion in the relation of rumination to psychological flexibility. The study is designed according to Structural Equation Modelling (SEM). The study group determined by the convenience sampling method consists of 470 university students aged between 18 and 28 who continue to study at various universities in Turkey as of 2022. In this study, the scores obtained from the psychological flexibility scale were evaluated as a reflection of acceptance. According to the results of our research, as the rumination scores increase, the acceptance scores from the psychological flexibility scale decrease. The relationship between the scores obtained from the psychological flexibility scale and cognitive defusion scores was moderately negative. The relationship between rumination and cognitive defusion scale scores was moderately negative. The mediation analysis demonstrates that rumination negatively affects psychological flexibility (acceptance), accounting for 38% of the change in psychological flexibility. The indirect effect of rumination on psychological flexibility scale scores was also significant. Cognitive defusion partially mediates rumination's effect on psychological flexibility (acceptance) scale scores. Rumination and cognitive defusion explained 47% of the change in psychological flexibility scale scores representing acceptance.

Rumination, psychological flexibility, cognitive defusion, university students.