Abstract: A method for the determination of veterinary antimicrobial agent enrofloxacin, ciprofloxacin, sarafloxacin and difloxacin in fish muscle, using enoxacin as internal standard, has been developed. The influence of different separation conditions, such as the buffer, pH of the electrolyte and the organic added to the electrolyte was studied. The most suitable buffer is Na2HPO4-citrate at pH 5.0 containing 10%(v/v) acetonitrile. Clean-up and pre-concentration of the samples were effected by C18 solid-phase extraction and determination was carried out by capillary electrophoresis using a photodiode array detector (275nm). The calibration graphs are linear for the four fluoroquinolones from 25 to 400 μg/kg. The method recoveries for enrofloxacin、ciprofloxacin、sarafloxacin and difloxacin are 75.2%、79.7%、80.1%、79.2%. The limit of detection for Enrofloxacin is lower than 25 μg/kg, and the other are 25 μg/kg. The Rsds for intraday and interday are not more than 13.5% and 12.3%, respectively. It is a fast and simple method that allows the detection of positive muscle samples.