The middle of the 20th century was marked by the intense relationship between the United States and the Soviet Union. During the 1939 and with the beginning of the World War II, President of the United States of America, Franklin Delano Roosevelt, expressed his interest in helping the Soviet Union in the war against fascist regimes, arguing that the defense of the Soviet Union of Germany was crucial to US security and thus led the American people out of an isolationist state that had marked US foreign policy years before. Soon after the United States entered the war, the relations between the two countries strengthened and the countries continued to strive for the same goal - to win against hostile fascist regimes. During the war, the fundamental differences between the capitalist and communist regime were put into another plan. With the arrival of Harry Truman in power in the United States and the victory of the Allies in World War II, the situation changed and the US-Soviet relations move from an intense relationship to unstable and hostile one. After the war, each country tried to expand its influence in the world, which continued to increase the rivalry between the two states and ultimately led to the beginning of the Cold War. The aim of the thesis "The Analysis of US-USSR Relations during Roosevelt's and Truman's Presidency" is to explain that the state of affairs during the Second World War changed amicable relations between the United States and the Soviet Union to opposing ones and that the national interests of both states prevailed with the international relations during the 20th century. The thesis covers the period from 1939 to 1949 and describes US-Soviet relations in the context of international circumstances before, during and after the Second World War.