The aim of this paper is to highlight the key parameters of the parliament capacity as an institution of the political system as illustrated by studying the process of exercising state power in modern Ukraine. The strengthening of threats to the national security of Ukraine, which occurred since the beginning of the full-scale armed aggression against our state, has actualized, among other things, the problems of the institutional stability of its political system and the institutional capacity of its legislative power institution. To date, as an important component for completing the democratic transformation of the political system, mainly the institutial capacity of civil society institutions is considered in the Ukrainian research space, as highlighted in the articles by M. Stasyshyna, A. Kostenko, K. Petrenko et al. Methods used in the study: the analysis of the specified components of institutial capacity can be implemented based on the application of the research directions provisions of the new institutionalism of political science: international institutionalism, normative institutionalism and sociological institutionalism; and institutional capacity – based on the application of the research directions provisions of institutional studies in economics and political science and the new institutionalism of political science: classical (old) institutionalism, structural institutionalism and economic institutionalism.