Abstract: The present article is devoted to business structurse as socio-economic systems that function in the pharmaceutical sector. The authors provide information about market shares held by the leading pharmaceutical companies in 2015. Business entities and structures are being viewed from the point of view of socio-economic systems. The subject of the research is the development of the microlevel of socio-economic systems (business entities) taking into account peculiarities of the pharmaceutical sector. The authors provide a description and classification of peculiarities of such business, define the term 'socio-economic system' and describe particularities of managing changes in pharmaceutial business entities. The authors have used the method of the ascent from the abstract to the concrete that implies conditional dismembering a research object and description of all its features using a number of terms and characteristics. The main results of the research are the following: systematization of pharmaceutical business entities according to three indicators (market, economic and political-legal; description of pecularities of managing changes at pharmaceutical business entities (complex structuralization, integrativity, possible elements with different targets, goals and development paths); and division of the research subject into two parts: pharmaceutical business entities and environment as well as description of the intensivity of interaction between these entities and environment.