Abstract: In his research Rakov examines problems of requalifying taxpayer's profits and operations in order to prevent tax avoidance in BRICS countries based on the example of Brazil and russia. The author of the article carries out a comparative analysis of taxation rules and standards in the aforesaid countries, defines general principals of legal regulation in the sphere of tax avoidance prevention and outlines different approaches to legal regulation of particular issues related to tax regulation. In his article Rakov analyzes doctrinal approaches of Russian and foreign academists to the topic and describes the main legal views that have been formed in the legal practice regarding the matter. When anlyzing the problems arising in the process of requalifying taxpayer's profits and operations for the purpose of tax avoidance prevention in BRICS countries, the author has used comparative law, technical method as well as the method of legal forecast. The author outlines the problem of uncertain borders of discretionary powers of tax authorites aimed at changing the legal qualification of taxpayer's profits and operations for the purpose of preventing tax avoidance. Based on constitutional and tax provisions and laws, the author have formed the principles of preventing tax avoidance. Based on the results of the comparative analysis of Russian and Brazil laws, the author has also established the main vectors of developing the legal regulation in the sphere of taxes and cooperation between two countries as parts of BRICS.