Abstract: Ciprofloxacin is a chinolone antibiotic, which is used mainly in the treatment of urinary tract infections but also in pulmonary tract, prostate gland, bone and bone marrow infection. Ciprofloxacin is also known for its anticancer in vitro properties. In this study hamster ovarian cancer line CHO AA8 was used for evaluation of cytotoxic properties of ciprofloxacin against neoplastic cells. For this purpose we used different concentrations of ciprofloxacin range from 10 to 1000 microg/mL. Cell viability was counted using trypan blue assay. Ciprofloxacin induced morphological changes and decreased viability in a concentration and time dependent manner within CHO AA8 cells. In low concentrations cytotoxic effect of ciprofloxacin is weak only after 24 h incubation. In the highest concentration of ciprofloxacin, after 24, 48 and 72 h incubation only a very small number of living cells (not exceeding 1%) was observed. No living cells were observed after 96 h of incubation times and ciprofloxacin concentrations of 800 and 1000 micrpg/mL. These promising results deserved future studies on chinolones and ovarian cancer.