In an attempt to develop potent and selective antitumor agents, a series of liquiritigenin thiosemicarbazone derivatives were designed and synthesized. The cytotoxicities of these compounds were evaluated in vitro against K562, DU-145, SGC-7901, HCT-116 and Hela cell lines. The pharmacological results showed that most of the prepared compounds displayed excellent selective cytotoxicity toward K562 and DU-145 cells. From the structure-activity relationships we may conclude that the introduction of a thiosemicarbazone functional group at the 4-position in the skeleton of liquiritigenin is associated with an increase in cytotoxicity.