This paper provides detailed analysis of the so-called ‘Rusk Letter’ which has been generally referred to as an evidence of Japan’s territorial claim to Dokdo island. The Rusk Letter is a diplomatic epistle which was drafted by Dean Rusk, the US Assistant Secretary of State and sent to the Korean Embassy in the US on August 10, 1951. This letter considers Dokdo as Japan’s territory. However, the Rusk Letter has been legally and historically criticized from mainly two aspects. First, the Rusk Letter referred to the ownership of Dokdo only considering the Japanese position which was not true. Second, this letter was a confidential and unofficial document which was sent only to Korea; Japan and even the US Embassy to Korea did not know the Rusk Letter. It did not influence on the decision of Peace Treaty. Therefore, the Rusk Letter cannot be a critical evidence of Japan’s territorial claim over Dokdo.