This research seeks to identify the effect of shareholders concentration on risk-taking behavior of Iranian private banks over the period 2008-2014.We used Herfindahl-Hirschman Index as proxy for concentration. The banks’ risk-taking is represented by Z-score. The model is estimated on a panel of 10 commercial banks from Iranian private banks. In addition the bank size, interest marginal revenue, Interest activity, capital reserve and non-current loans are considered as controlling variables. The results show that shareholders concentration could mitigate banks risk. Among the control variables, bank size has positive and capital reserve have negative impact on risk-taking of private banks.