Finding the suitable capital structure for small and medium size enterprises, SMEs, is vital. A suitable capital structure helps SMEs to stay alive in the competitive market and has a positive effect on the national economy. Wealth maximization is the first objective of the firms, and capital structure proposition shows how a firm plans to finance its projects to meet its first objective. The purpose of this thesis is to investigate the impact of the capital structure determinants on the SMEs borrowing behavior. SMEs in this research are defined as the small independent privately held firm with less than 250 employees.

In order to reach the purpose of this thesis, I have consulted the relevant theories of capital structure. By the support of the earlier studies, as well as the related theories, I have developed the testable hypotheses to examine the impact of capital structure determinants on the decomposed leverage level. To conduct this thesis, I have used the deductive approach, which is a similar approach suggested by the key reference of this study, Michaels et al (1999).   Size, age, profitability, growth, operating risk, and asset structure are selected as the determinant of capital structure. With the unique set of data gathered from 201 SMEs in Iran over the period of 2006 to 2010, the statistic panel data regression is used to analyze the empirical data. To investigate the borrowing behavior of the SMEs comprehensively, the observed SMEs were picked up from different manufacturing industries in Iran.

The result of this research reveals that the impacts of capital structure determinants on SMEs leverage levels are different in terms of both magnitude and direction. The result indicates that profitability has a strong impact on SMEs borrowing decisions. Besides profitability, size and asset structure appear to have an impact on leverage level in compare with other determinants. This thesis finding shed lights on the necessity of using the maturity structure of debt (short-term debt and long-term debt) as dependent variables. Firms are more willing to finance their projects with short term debt, rather than long term debt. Long term debt is costly, and the probability of bankruptcy is higher with long term debt. Although long term debt is riskier for SMEs, but it shows the management confident in the firm’s future since it obliges the firm’s management to make legally binding future payments of interest. However, the empirical result of this study shows that all the determinants have an effect on the level of leverage in SMEs.