The present invention relates to a novel diaminedithiol derivative or a pharmaceutically acceptable salt thereof; radiorhenium or radiotechneticum complex thereof; a composition for treating liver cancer comprising the radiorhenium complex and lipiodol; and, a preparative kit of the composition for treating liver cancer.In the composition according to the invention, the diaminedithiol derivative is a novel compound in which long chain alkyl groups were introduced to diaminedithiol, capable of forming a radiorhenium or radiotechnetium complex thereof with an ease and leading to stronger van der Waals bonds with lipiodol. As a result, the complex becomes more stable in a medium, lipiodol, whereby the composition of the invention exhibits a high accumulation rate in liver cancer tissue when injected via hepatic artery, thereby capable of achieving an efficient treatment of liver cancer.