Conservatism has emerged as one of the practical principles in the development of accounting standards. In recognizing profits and losses, accountants desire more validity for good news (profits) than for bad news (losses). Accordingly, conservatism is the product of asymmetry in the income statement verification. In this research, a comprehensive investigation is conducted on the impact of financial leverage and the composition of the board of directors (the board) on accounting conservatism in firms listed on the Tehran Stock Exchange (TSE). Board combination was examined using board independence criteria, board size, and CEO duality. Moreover, to measure conservatism and the effects of independent variables on it, Basu’s model (Default-Adjusted-Basu) modified by Khan and Watts (2007) was used. In this research, the impacts of variables which were expected to have an influence on the relationship between independent and dependent variables, namely firm size, financial leverage, and the price/book ratio, were controlled. A number of 72 firms listed on the TSE constituted the population of the study and were studied based on their financial statements for the period 2006-2010. To test the hypotheses, correlation test and multivariate regression analysis were used. In general, the results are indicative of a significant relationship between board independence and accounting conservatism but there is no significant relationship between CEO duality and board size with conservatism.