The paper aims to expose the main argument of the constitutional thought of Donato Giannotti. In the great crisis of the last republic of Florence (1527-1530) and the possibility of the revival of a free system of government, Giannotti is the most influential republican theorist of his generation. He produces an overlook of the Republic of Venice in order to understand and create a new regime for his city. But, in doing so, he dialogues with the thought of Savonarola and Machiavelli, who had wrote about the advantages and disadvantages of the aristocratic republicanism of Venice. The point of innovation of Giannotti in this intellectual context is that he aims to equalize all the political spaces in a new interpretation of the mixed government. To conclude, I sustain that his approach is not only important to the development of the electoral systems of modernity, but also to the liberalization of each one through each social group. Finally, Giannotti, in doing so, appears to be the most democratic republican thinker of the Italian Renaissance.