This qualitative study was carried out to investigate the effectiveness of cognitive-behavioral therapy (CBT) for Iranian migrants suffering from major depressive disorder (MDD) and living in Austria for an average of 14 years. The qualitative data were collected through interviews based on the Farsi version of the Structured Clinical Interview for the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). However, to obtain more information from the participants, they were asked to talk in more detail about their childhood and teenage years, reasons for immigration, their lifestyle before and after immigration, and their social activities. Interviews were conducted at four time points: preintervention, postintervention, 1-month follow-up, and 6-month follow-up. Patients who did not complete the interventions were interviewed on a voluntary basis to explain their reasons. Preintervention interviews were conducted to get some useful information about participant's' expectations of psychotherapy, especially group-based cognitive-behavioral therapy (GCBT), and also to assess the reasons for depression from their own point of view. The postintervention interviews were conducted to examine the participants' psychological situations as well as the reasons for positive effects of interventions. The interviews on average lasted 50 minutes, and field notes were taken. The results of this study showed a reduction in depression symptoms after the interventions. However, the effect of treatment was not persistent. The findings suggest that the main reasons behind Iranian migrants' depression in Austria is related to their dysfunctional acculturation attitude. The effectiveness of GCBT for Iranian migrants with depression also may be related to their sociocultural background.