The capital structure shows the way in which a particular company is financed. This paper examines the optimal combination of equity and debt sources, i.e. which of the five selected companies is financed equally by equity and debt. This research question is examined because the ratio of equity and debt sources to the total liabilities of the company is important. The problem that arises when there are not enough sources of equity is the increased risk that the company will become insolvent, i.e. that the company will not be able to meet its obligations to other entities in a timely manner. The companies for which the analysis of the capital structure was carried out are located in Osijek-Baranja County and fall into the category of medium and large companies. The period for which the research was conducted is from 2017 to 2021. In order to conduct the research, an analysis of the financial statements (balance sheet and income statement) was conducted using financial indicators, as well as a horizontal and vertical analysis for each company separately. The objective of the paper is to determine the best ratio of capital and liabilities to total liabilities of the company. In order to find an answer to the research questions, the concept of capital structure was considered first from a theoretical and then from an empirical point of view. The most popular theories of capital structure are discussed in the paper: Modigliani-Miller theory, traditional theory, agency theory and models based on asymmetric information. Based on the research conducted, it can be concluded that there are differences in the capital structure of the observed companies. Some of the observed companies finance themselves more from their own sources and less from external sources, while the situation is reversed for other companies. Each company should find an optimal combination of financing sources that does not affect the liquidity and profitability of the company.