Abstract: To discover novel antitumor fluoroquinolone lead compounds from a rational modification for antibacterial fluoroquinolones, a fused heterocyclic ketone corresponding to thiazolo2,3-b1,2,4triazolone used as a bioisosteric replacement of the C-3 carboxylic acid group of ciprofloxacin 1, and further modification by a Claisen condensation reaction with substituted benzaldehydes formed novel fluoroquinolone C-3 fuse heterocyclic α, β-unsaturated ketones as the title compounds (6a-6r), separately. The structures of eighteen title compounds were characterized by elemental analysis, ¹H NMR and MS, and the in votro anti-proliferative activity against human hepatoma Hep-3B cells, pancreatic Capan-1 cells and leukemia HL60 cells was evaluated by a MTT assay. The preliminary results showed that the title compounds not only had more significant anti-proliferative activity against three tested cancer cell lines than that of the parent ciprofloxacin 1, but also exhibited the highest activity against Capan-1 cells. In particular, compounds carrying an electron-withdrawing carboxyl (6k, 6m) or sulfonamide substituent (6q, 6r) attached to benzene ring were comparable to or better than constractive drug doxorubicin against Capan-1 cells. As such, it suggests that it is favorable for a fused heterocyclic α, β-unsaturated ketone scaffold instead of the C-3 carboxylic acid group to improve the antitumor activity of fluoroquinolones.