The Brazilian social thought sought, throughout the past century, to understand the processes of change in the country, especially the relation between the State and the society. In that sense, the phenomenon of populism gained prominence, due to its implications in the electoral process, the renewal of political leadership, and even in the area of public finance. This work tried to discuss the interpretations on the populist manifestations during the period from 1945 to 1964, proposed by the School of Sociology of the University of São Paulo, by the Superior Institute of Brazilian Studies, and by representatives of the liberal economic thought. It was possible to verify that the studied contributions pointed out the relevance of populism studies for better understanding Brazilian politics during the period from 1945 to 1964, as well as helped to spread the discussion about the phenomenon of populism in the public sphere. However, as a consequence of the distinct fundamentals through which different theoreticians based their analyses, they had not been able to accomplish to a precise definition of the phenomenon. In the School of Sociology of the USP relevant concepts were state of commitment developed by Weffort and the search for understanding the decrease of the importance of class struggle during the populist period. On the other hand, the intellectuals of the ISEB had worked under guidance of CEPAL`s thought. They saw Populism as a phase in the evolution of the country, and emphasized the concern with national development. The liberal economic thinkers were loyal to economic liberalism, criticizing governments that did not give priority to fiscal balance.