This research aim to investigate the relationship between capital structure and firms life cycle in Tehran Stock Exchange. Sample of research consists of 187 firms listed in Tehran Stock Exchange during the period between 2007 to 2013. In this study, firms are divided into two groups of growing firms and mature firms and firm’s capital structure consisted of net debt, retained income and equity capital. The results show that the effect of financing deficiency on net debt in growing firms is more than mature firms. In addition, growing firms follow Pecking Order Theory (TOT) more than mature firms but it is insignificant