Abstract: Ciprofloxacin (CPXC) in roast eel sample was extracted twice with acetonitrile acidified with formic acid (1+99).The supernatant liquid was collected and diluted to 25.0 mL with acetonitrile.An aliquot of 10 mL was taken,dried by blowing with nitrogen at 40 ℃ and the residue was dissolved in 2.0 mL of the mobile phase solution,which was further extracted with 2 mL of n-hexane.Ten μL of the lower layer was taken and introduced into the HPLC/MS analyzer.In HPLC,the XBridgeTM Shield RP18 column (250 mm×3.0 mm,5 μm) was used as stationary phase,a solution containing methanol,acetonitrile and dil.formic acid (2+998) mixed in the ratio of 15+15+70 was used as mobile phase,and fluorescence detection at λex 275 nm/λem 445 nm was used in the determination.In MS,SIM technique under the mode of ESI(+) was used for the detection,and the quantitative ion used was m/z 331.9M+H+.Linear relationships between the values of peak area of detection signals and concentration of CPXC were obtained in the ranges of 100.0-2 500.0 μg·L-1 for HPLC-FD,and 20.0-500.0 μg·L-1 for MS-SMI-ESI(+),with detection limits of 50.0 μg·kg-1 and 10.0 μg·kg-1 respectively.Tests for precision and recovery were made by addition of standard solution of CPXC at 3 different concentrations.Values of RSD′s (n=6) found were less than 6.5% and values of recovery in the range of 83.0%-99.0%.