The article is devoted to the development and approbation of a methodological approach to the modelling of an optimal structure of a joint stock company. The optimal capital structure is defined by the authors as a combination of debt and equity, which maximizes the overall value of the company. The article contains the main conclusions received from different economic researches on the optimization of a capital structure. The authors invented a model of the optimal capital structure that may be used by the joint stock companies in emerging markets with greater risk due to political instability, domestic infrastructure problems, currency volatility and limited equity opportunities. This model is supplemented with corrective indicators of financial risks.