Introduction. Peculiarities of functioning and structure of the stock market of Ukraine play an important role in ensuring the state economic security and, in particular, financial. The purpose of the article is to analyze the state and features of the modern stock market of Ukraine, to investigate its impact on the state of financial security of the country. Results. Imbalances in the primary securities market are due to the small number and volume of issues, as well as the predominance of issuers of state banking institutions and state corporations, which carried out the issue to keep banks at the required level of capital and replenishment. The volume and number of bond issues are significantly lower compared to stocks. There are currently four exchanges in Ukraine, but primary stock market operations are focused on the PFTS. The secondary securities market of Ukraine is more developed in Ukraine (the total amount of transactions is more than 90% of the volume of exchange contracts during the entire analyzed period). Transactions are carried out mainly on stock exchanges – PFTS and “Perspective”. The trend of the results of the secondary stock market has improved (significantly decreases the value of indicators – linear deviation, variance, oscillation coef­ficient), however, the value of the oscillation coefficient still indicates a lack of homogeneous and balanced environment. Approximations to the state of homogeneity can be characterized by stock exchange contracts concluded on government bonds. At the same time, the volume of concluding exchange contracts is generally insignificant, and the share of exchange contracts on government bonds in total is approaching almost 100%; therefore, it can be concluded that the entire stock market is characterized by significant heterogeneity and imbalance. Conclusions. The stock market of Ukraine does not fulfill its key function – investment. The stock market of Ukraine is characterized by pronounced imbalances. At the same time, it should be emphasized that the structure of the stock market is characterized by dynamic processes, so the creation of a fully balanced environment can not be a priority. The stock market of Ukraine mostly serves the needs of the public sector of the economy and in no way contributes to the de­velopment of not only the real but also the financial sector of the economy. That is, the security of the stock market is directly related to the security of debt and budget, which are components of the financial security of the state.

When forming the optimal capital structure, the choice of methods, approaches, tools is important, which is determined by a set of initial conditions, the need to perform the tasks, achieving results / strategic guidelines. The purpose of the article is to systematize scientific approaches to optimize the capital structure, to clarify the impact of factors on the capital structure of the corporation, which will serve as a basis for ensuring the optimal level of capital structure. As a result of the research, the views of scientists on the optimization of capital structure are systematized, the key aspects of the three main approaches to such optimization are singled out and described. The approaches used in determining financial leverage are described. The expediency of determining financial leverage through the ratio of EPS – earnings per share and EBIT – earnings before interest and taxes is substantiated. The most common methods of capital structure optimization are identified: the method of capital expenditures (the method of minimizing the weighted average cost of capital); the method of determining the effect of financial leverage or the method of maximizing the level of financial profitability; method of determining the complex operational and financial leverage; EBIT-EPS valuation method, Du Pont method, operating profit method and adjusted present value method. Their features, advantages and disadvantages of use are described. The factors influencing financial leverage are systematized, the positive or negative influence of each of the determined factors on financial leverage is determined. A matrix of factors that determine the optimal capital structure in terms of the environment (internal or external) and the implementation of financial policy (at the strategic or operational-tactical levels).