In this study, it is investigated the psychological effects of yoga on adult’s mood such as stress, anxiety and depression. Depression, Anxiety and Stress Scale (DASS) with 42 items (Lovibond and Lovibond, 1995) was used for collecting data in two times: Pre-test and Post-test. This scale administered in 95 subjects in Middle East Technical University in Ankara/Turkey.  For data analysis, SPSS version 21 and a paired sample T-test were used. The results indicated that there was a significant difference between stress, anxiety and depression scores before and after two weeks yoga exercise treatment. Yoga has a positive effect on person’s psychological mood and it may decrease the stress, anxiety and depression disorders.