This paper aims to analyze the true purpose behind Britain’s diplomatic policies to open Korea, undertaken by British diplomats in East Asia in the mid-19th century. When the Crimean War broke out in 1854, the British-French combined fleet attacked the Russian military and naval base at Kamchatka; at the time, John Bowring, Governor of Hong Kong, made a proposal to the 4th Earl of Clarendon, Secretary of State for Foreign Affairs in UK, to open Korea, together with European powers. In 1865, Thomas Wade, the British Minister to China, made plans to open Korea in association with other European powers in order to deter Russian aggression towards Korea. The reason that British diplomats chose to open the doors of Korea was to protect British commercial interests in East Asia by blocking the exclusive entry of Russia. By undertaking the opening of Korea, in association with other European powers, they attempted to make Korea a place where shares of interests were equally divided. However, since Korea was known to be a vassal state of Qing, Britain was required to check whether or not Korea had its own sovereignty. British diplomats confirmed that although Korea was a vassal state, she had sole responsibility for internal and external affairs. Britain therefore began to regard Korea as an independent state.