Davoud Eftekhar Nahli - Department of bank accounting, Iran Banking Institute, Tehran. Iran
Hamed Shadkam - Department of bank accounting, Iran Banking Institute, Tehran. Iran
Peymn Noori Broojerdi - Department of bank accounting, Iran Banking Institute, Tehran. Iran

With the entry of non-governmental banks into the country's banking system in ۲۰۰۱, significant changes took place in the Iranian banking industry. So that the decrease in the degree of concentration indicates the strengthening of the competitive environment in the country's banking scene. Inadequate risk management has made banks more inefficient in the form of non-current receivables and other financial crises. The existence of non-current receivables reflects the growing trend of this managerial weakness.The main purpose of this study is to investigate the effect of bank ownership concentration on Non-performing loans ratios of accepted and unaccepted private banks in Tehran Stock Exchange. For this purpose, four criteria of concentration of ownership (loan growth ratios, concentration, size and efficiency) of banks as well as Non-performing loans ratios for a nine-year period between ۲۰۰۳ and ۲۰۱۱ have been examined. The statistical sample of this research is the banks that have audited financial statements for at least three years.Therefore, after gathering the theoretical foundations of the subject and formulating research hypotheses, information was collected and prepared. Library methods, financial reports and audited financial statements of banks were used to collect information. Panel data method was used to test the hypotheses and Eviews ۶ software was used for statistical analysis. In general, the research findings show that the concentration of bank ownership has a positive and significant effect on Non-performing loans ratios.