Zagrebačka banka d.d. is the leading bank in the Republic of Croatia and part of the UniCredit Group. The subject of this paper is the business, strategic and financial analysis of Zagrebačka banka d.d. in imperfect oligopoly competition, i.e. analysis of the impact of oligopoly conditions on the company’s operations and the strategic group within which the company operates. The primary goal of the work is to analyze the strategic and financial factors of success to diagnose the current state of the company and the connection between the degree of imperfect competition on the banking market and the achieved results of the company. The first part of the paper will present the specifics of bank operations under oligopoly conditions through a historical review of the banking industry, its regulatory framework, impact on operations and limitations, and the very economic efficiency of banks in the Republic of Croatia. The conclusions from the first part will be used as a basis for the analysis of the external environment of Zagrebačka banka d.d. in the second part of the paper. In the third part of the work, the internal environment of the company will be analyzed and a financial analysis of its reports will be made. All the information collected through the analysis will be used to carry out the analysis of the bank oligopoly in the Republic of Croatia, viewed as a strategic group of banks with the largest share of concentration on the market.