In the pre-negotiation stage, the most difficult obstacle to start the Japan-Soviet normalization negotiation turned out to be the issue of the Japan-US Security Treaty. While Japan regarded it as the most fundamental framework to realize its security, the Soviet Union did not change its position that the Treaty was an obstacle to start Japan-Soviet negotiations. This article investigates what kinds of discussions were held within the political leadership of the Soviet Union on the positioning of the Japan-US Security Treaty in the process of normalization with Japan. An analysis of declassified Soviet archival documents reveals the following five points. First, the Korean War changed the Soviet Union’s perception of the threat posed by the US forces stationed in Japan, and the role of the Kuril Islands in their defense policy changed accordingly. Second, as for the issue of peace with Japan, the division in the Soviet Union’s political leadership after Stalin’s death was most evident in the question of whether or not to accept the Japan-US Security Treaty. Third, the Soviet Union entered into negotiations with differences in opinion on this point. Fourth, after the start of negotiations, the political leadership of the Soviet Union, headed by Khrushchev, overturned Foreign Minister Molotov’s negotiating stance of not accepting the Japan-US Security Treaty, and made a decision to “accept” it under certain conditions. Fifth, the Soviets’ proposal on transferring Habomais and Shikotan islands to Japan was closely related with their decision to “accept” the Japan-US Security Treaty.