The aim of this study was to investigate the possible cytotoxic and apoptotic effects of a fluoroquinolone (FQ) antibiotic, ciprofloxacin (CPFX), on HeLa and HeLa-tat cell lines. The cultured cells were incubated with three different (20 to 100 mg/L) concentrations of CPFX, and cytotoxicity was determined by trypan blue test. A dose- and time-dependent decrease in cell proliferation was observed for both cell types except 50 to 100 mg/L CPFX for 24 h for HeLa-tat cells. CPFX-induced apoptosis was also measured by the acridin orange-ethidium bromide staining using a fluorescence microscope in both cell types. Our results showed an induction of apoptosis at 100 mg/L concentration of CPFX after 24 and 48 h of incubation in both cell types. These data confirmed our previous studies obtained with normal human fibroblast cell cultures and indicated that CPFX induces cytotoxicity and apoptosis in HeLa cells.