Abstract: To explore a new strategy for further optimization to the C-3 bioisteric heterocyclic ring of fluoroquinolones, twelve novel fluoroquinolone C-3 s-triazole Schiff-base carboxylic acid derivatives( 7a - 7l )were designed and synthesized with both functionalized sulfanylacetic acid and Schiff-base moieties as the modified side-chain for the C-3 bioisosteric s-triazole ring of pefloxacin( 1 ). The structures were characterized by elemental analysis and spectral data, and the in vitro anti-tumor activity of the title compounds against SMMC-7721, L1210 and HL60 cell lines was evaluated. The preliminary pharmacological results demonstrated that the title compounds possessed more significantly anti-proliferative activity than either the parent 1 or the corresponding amine intermediates( 6 ). In particular, the title compound bearing a fluorine atom( 7j )and compound bearing a nitro group attached to benzene ring( 7l )were comparable to the control doxorubicin against SMMC-7721 cells with an IC₅₀ value of micro-molar concentration, respectively. It suggests that s-triazole ring modified with functional side-chain moieties instead of the C-3 carboxylic group is favorable to the improvement of antitumor activity.