DW-116 {(1-(5-fluoro-2-pyridyl)-6-fluoro-7-(4-methyl-1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid hydrochloride) is a new quinolone antibiotic with a broad antibacterial spectrum against G(+) and G(-) bacteria. DW-116 was evaluated for the appearance of micronucleus in polychromatic erythrocytes (PCEs) of mouse bone marrow cells after intraperitoneal and oral single administration. We prepared the bone marrow cells at 30hr after drug administration and they were used for measuring PCE with micronucleus. The results showed there was no statistically significant increase in the numbers of PCEs with micronucleus in all DW-116 administered groups compared with a negative control group. The results also showed that the ratio of normochromatic erythrocytes(NCEs) to PCEs of all DW-116 administered groups was not significantly different from that of a negative control group. These results suggested that DW-116 may not cause any chromosomal damage and it has no in vivo mutagenic potential under these experimental conditions.