In this research, it was paid to the investigation the relationship between board efficiency and accounting conservatism of listed companies in Tehran Stock Exchange during 2006-2012. To do this study, 109 listed companies in TSE were selected in mentioned period. Pooled/panel regression analyses in software EViews 6 were applied to test of research hypotheses. Exerted independence variables are different criteria of board efficiency contain CEO Membership in Board (CEOMB), Outside Board (OB), Board Ownership (BO), Financial Specialist in Board (FSB), and No. Meetings of Board (NMB). The dependent variable is Conservatism Index (CI) based on Givoly &Hayn (2000) model in this study. Also, company size (SIZE), financial Leverage (LEV), and Market to Book Value (MTB) were applied as control variables. Findings indicate that the effect of OB on CI is positive and significant in total companies level. Other results show the positive and significant effects of SIZE and MTB on CI, and the negative and significant effect of LEV on it.