OBJECTIVE:To observe the stability of fleroxacin injection. METHODS: The contents of fleroxacin injection and its degradation product were determined by HPLC method,and the effects of light, heat, pH value and halogen ion on the stability of fleroxacin injection was also studied. RESULT: The average recovery rate of the fleroxacin was 100.4%(RSD=0.87%); the color of fleroxacin injection deepened and the content of the degradation product increased if its pH value was lower or if the illuminating or heating time became longer; the sediments were separated out if met with halogen ion. CONCLUSION: The fleroxacin injection was unstable and easy to decompose under light and heat, especially under the light; the content is more likely to be decomposed if the pH value is lower;fleroxacin injection can not to be applied together with the halogen ion.