In view of the importance of the sources of financing of the Brazilian companies, and taking into account the context of particularities and characteristics of the Brazilian market and the context of low international interest rates, this work aims to analyse the determinants of capital structure of Brazilian companies listed in Bovespa (Bolsa de Valores de São Paulo) in the period between 2004 and 2006. One should bear in mind that the period under study was not typical, once the IPOs in Brazil were reborn in 2004 and remained heated in the last three years, contrasting with the Pecking Order Theory, which defends that the last financing alternative would be the issue of shares. According to this theory, the entrance of new shareholders is avoided to the last extent. However, between 2004 and 2006, 81 companies used the stock market for funding and most of them did not have high levels of debt and remain nowadays with low net debt. This study also aims to investigate if there is a difference between the determinants of capital structure, in case larger and smaller companies are discriminated. The theories studied encompass the cost of agency theory, the pecking order theory, the fiscal theory, the signaling theory and the trade-off theory. Out of the many factors determinants of the capital structure proposed, we selected a few of them, mainly quantitative, to analyse empirically its relevance and validity. The factors in question were: the influence of control, company size, profitability, assets tangibility and growth opportunities concerning the Brazilian companies.