This research focuses on the most important problem of the cost accounting organization process–the problem of choosing cost groupings formed in accounting and reporting called cost accounting objects. The research aims to identify, describe, and justify the principles for choosing a cost accounting object. During the research, the authors used various research methods, including analysis, synthesis, generalization, thought experiment, deduction, induction, tabular, and graphical methods. As a result, the authors formulated four principles for selecting cost accounting objects; each principle of choosing was justified. The scientific significance of this research is the development of approaches to organizing cost accounting in terms of streamlining and scientific justification for choosing cost accounting objects. The practical significance of this research paper is the development of the procedure for implementing the requirement of rationality as one of the requirements for setting up and maintaining records.