The residues of fluoroquinolones in Olive flounder (Paralichthys olivaceus) and Black rockfish (Sebastes schlegeli) were investigated after oral doses of 20 mg/kg for 30 days. Blood samples were taken at 5 hours, 10 hours, 1 day, 2 days, 3 days, 5 days, 7 days, 9 days, 13 days, 20 days and 30 days after treatment. The concentrations of fluoroquinolones were detected by high performance liquid chromatography using a UV detector. The recovery rates of fluoroquinolones in fish samples ranged from 92.0-99.7%, 93.4-97.5% and 93.0-97.9% for treatment of 0.1, 0.5, and $1.0{mu}g/g$, respectively. Ciprofloxacin, enrofloxacin, norfloxacin and sarafloxacin were detected in the blood of the olive flounder at 10 hours, 10 hours, 1 day and 10 hours after treatment with $6.43{mu}g/g$, $6.07{mu}g/g$, $11.83{mu}g/g$ and $11.02{mu}g/g$ as maximum level, respectively. Ciprofloxacin, enrofloxacin, norfloxacin and sarafloxacin were detected in the blood of black rockfish 1 day, 1 day, 1 day and 10 hours after treatment with $8.26{mu}g/g$, $8.03{mu}g/g$, $7.29{mu}g/g$ and $9.38{mu}g/g$ as maximum level, respectively. However, ciprofloxacin, enrofloxacin, norfloxacin and sarafloxacin were not detected in olive flounder samples at 20, 30, 20 and 20 days after treatment in any experiments (<LOQ). Additionally, ciprofloxacin, enrofloxacin, norfloxacin and sarafloxacin were not detected in the black fockfish samples at 13, 20, 13 and 13 days after treatment in all experiments (<LOQ).