Credit rating of some country is a significant indicator of development and has a significant role for each country. Economic policy leaders seek to achieve a better credit rating, and in order to achieve this, it is necessary to determine which determinants are significant for credit rating. Determinants that have a significant impact on credit rating are not the same for each country. In this work, theoretically, and then empirically, is determined the importance of certain determinants for credit rating of developed and developing countries. The aim of the theoretical part is to determine the importance of credit agencies for the financial market and to analyze earlier research in order to better interpret the results obtained by empirical research. The main purpose of this research is to prove are determinants listed in two hypotheses crucial for a particular group of countries. The determinants that are crucial, in the empirical part of the work, have been statistically significant for the models they appear in. The most important determinants for the credit rating of developed countries are: GDP per capita, current account balance, public debt and unemployment. In developing countries, they are: GDP per capita, budget deficit, inflation and real GDP growth. Thus, all the determinants that were detected as crucial in earlier researches, are not crucial in this research. This is why is important to be careful at making decision, which can improve the credit rating of the country.