The purpose of this study was to determine the role of customer orientation and environmental uncertainty in relationship of entrepreneurial orientation and organizational performance of Tehran city Mellat banks. To achieve this aim, 172 managers and experts selected randomly from seven management areas of Tehran city Mellat banks and they completed entrepreneurial orientation (Hughes & Morgan, 2007), customer orientation (Donavan et al., 2004), and environmental uncertainty for commercial environment (Miller, 1993) questionnaires. Organizational performance was determined using two indicators included total income and pure profit in 2010 financial year. Results of structural equation modeling showed that structural relationships between entrepreneurial orientation, customer orientation, environmental uncertainty, and performance have acceptable fit with the collected data (c2=31.03, r=.176, RMSEA=.041, RMR=0.07, GFI=.92). In this model, entrepreneurial orientation directly (b=0.34) and indirectly through the customer orientation path (b=0.38) has significant effects on the organizational performance. The environmental uncertainty has not a significant effect on the entrepreneurial orientation and performance relationship, but negatively has a direct effect on the entrepreneurial orientation (b=-0.50). Finding of this study suggest that innovativeness, pro-activeness, and competitive aggressiveness are important determinants of Mellat bank performance. Service delivery and customer needs reinforce the effects of entrepreneurial orientation on performance, however; entrepreneurial orientation in these banks is influenced byenvironmental components.