The present study,The Impact of Private Equity Funds on the Cost of Capital of Invested Companies in Brazil, tries to combine elements from the theory of cost of capital with that of Private Equity/Venture Capital (PE/VC). Apart from performance improvements, it is expected that PE/VC funds influence short and long term valuation of companies through their influence in the cost of capital for invested companies. The weighted average cost of capital is estimated having the cost of equity based on adjusted Capital Asset Pricing Model (CAPM)and cost of debt based on the ratio between financial expenses and average loans, debentures and short and long term financial rents. The introduction of a dummy variable to account for PE/VC investment will indicate any impact of such participant on the cost of capital.The analysis of the impact of PE/VC may add to the discussion on the factors that influence Brazilian companies cost of capital.Estimated regressions show significant coefficients for most of the explanatory variables and confirm most of the expected signs. The dummy introduced to control for investment by PE/VC funds is significant at the 10 percent level with a positive influence on cost of capital. Such result indicates PE/VC funds may constitute an alternative source of financing that will influence the cost of capital on the equity share of that cost. Since studies carried out so far have done little to integrate both cost of capital and PE/VC theories, a quantitative estimate the impact of PE/VC on cost of capital will shed light on managers decision of funding sources.