Previous researches on Argonaut island has been limited to revealing basic information about the discovery of the island off the coast of Ulleungdo in the summer of 1791. This study aims to concretize the nautical life of the British explorer James Colenett, who found the ‘doubtful island’ Argonaut, and the background of his journey to the East Sea and his discovery of the Argonaut island. The results of this study are as follows: first, Colnett’s the second fur trade voyage was aimed at selling fur to China at the same time as it build a permanent foothold in Nootka, the hub place of fur trade on the northwest Pacific coast. Second, when the Colnett’s fleet entered Macao with sea otter fur on board, they turned to Korea and Japan to find a new market as the Chinese government imposed a fur trade ban. Third, Colnett tried to trade with natives of Korea and Japan, but his trial failed. However, when he tried to find out a trade port along the east coast of Korean peninsula, he found an island near Ulleungdo Island. And this discovery was reflected in various maps made in the West, and was disseminated for more than half a century. Fourth, the map of Aron Arrowsmith, which was produced in 1798, marked only the breaking point of the rudder of the Argonaut, but from the map of Arrowsmith of 1811, Argonaut island was drawn permanently. Consequentially, during the mid-19th century, Japan had coped the nautical charts produced in UK, and Takeshima and Matushima were put in the place of Argonaut island and Dagelet island in this process. Consequently, from the mid-19th century, the meaning of Matsushima have changed from Dokdo island to Ulleungdo island in Japan.