A series of N-[5-(chlorobenzylthio)-1,3,4-thiadiazol-2-yl] piperazinyl quinolones derivatives (4a-I) have been synthesized by reaction of piperazinyl quinolones with 5-chloro-2-(chlorobenzylthio)-1,3,4-thiadiazoles. Their structures were confirmed by elemental analysis, IR and NMR spectra. The antibacterial activities of 4a-I against a variety of Gram-positive and Gram-negative bacteria were determined. Several compounds showed a good antibacterial activity against Gram-positive bacteria among which, compound 4e with a 2-chlorobenzylthio moiety in ciprofloxacin derivative, exhibited high activities against Staphylococcus aureus and Staphylococcus epidermidis (MIC=0.06 ${mu}$g/mL). The structure-activity relationship (SAR) study revealed that the position of chlorine atom on benzyl moiety would dramatically affect the antibacterial activities of the synthesized compounds.