One of the most important issues in financing corporate is to find appropriate method to make a wise selection between getting loans and increasing the number of shares. There are different theories for making appropriate financing methods. The primary purpose of this paper is to investigate this issue based on market timing theory. The proposed model of this paper chooses selective companies from Tehran Stock Exchange. The proposed model of this paper uses regression analysis on two different models. The primary purpose of the first model given in this paper is to study the effect of market timing theory. In this part of survey, we measure the effect of the ratio of market value to book value on the sources of financing firms though increase in equities. Based on the results, we can conclude that as the ratio of market value to book value increases, firms tend to increase their equity though an increase to the number of shares. The first hypothesis of this paper is confirmed. The second model is associated with the relationship with mean ratio of market value on weighted book value and Leverage and the results of this paper do not confirm such relationship.