This paper investigates corporate governance and ownership effects on earning quality in Iranian private banks. The study uses the information of 12 private banks from year 2005 to 2010 using regression analysis based on panel data. Among different factors, the effect of big five shareholder are considered to be significant and positive on earning quality. In addition, the effect of one variable regression test reveals that institutional ownership has positive impact on earning quality. However, the impacts of other variables including percentage of ownership concentration, the size of board of directors, reliance on debt, logarithm of sum of assets, return of assets, logarithm of operating cash flow on earning quality are not meaningful. The result of this survey indicates that institutional ownership plays an important role earning quality simply because institutions normally have the access on professionals to control management.