The objective of this paper is primarily to compare and describe the development of the effective tax rate (relative tax burden) on the taxpayer earning only income from employment and emoluments in the Czech and Slovak Republics. The reason for choosing this type of income has been its importance in terms of the volume of tax collection in the area of natural persons income tax in the Czech Republic. The actual comparison has been performed for the years 2010, 2011 and 2012. In all cases, the legal status was considered that was valid and effective as of 31. 12. of particular year. Comparison of the effective tax rate was performed not only between the individual countries themselves, but also chronologically for individual countries (the Czech and Slovak Republics, respectively). After the general introduction, the relevant legislation as to incomes from employment and emoluments in both countries is explained. A separate chapter discusses the specification of the applied methodology, within which basic starting points and the simplifications applied are defined. Another part of the paper contains outputs from compiled mathematical models. These are presented in the form of graphic outputs and supplemented with commentary.