The article is devoted to the study of the so-called “Pisa's issue” of the politics of Florence at the turn of the XV-XVI centuries. The relevance of the topic is connected with the importance of the history of international relations and wars, such as interest to Machiavelli' diplomatic activity. The article deals with the facts related to the diplomatic activity of Machiavelli at the period of 1499-1500. The author comes to the conclusion about the important role of Machiavelli in the solution of the “Pisa's issue” by Florence.