In this paper, we examine relation between accounting losses and accounting conservatism over a 7- period in 48 loss firms in Tehran Stock Exchange. We report evidence that accounting conservatism and firm size have a positive relation and financial leverage has a negative relation with accounting losses. There is no relation between accounting losses and governmental ownership in study sample. Our findings contribute to the literature on accounting conservatism and they implicate that conservatism is likely to be an efficient financial reporting mechanism to increase firm value in a long term period because it restrict opportunistic payment to managers and other contracting parties. The increased firm value is shared among all parties to the firm increasing everyone’s welfare. In that sense, conservatism is an efficient contracting mechanism.