The pharmacokinetic properties of cefadroxil (CDX) were studied after oral administration for 7 days to cultured olive flounders (average 660 g), Paralichthys olivaceus. For examination of pharmaco-kinetic profiles, CDX of 45 to 225 mg/kg body weight was administered at two different water temperatures, $13{\pm}3^{\circ}C$ or $22{\pm}3^{\circ}C$. CDX concentrations were determined in muscle, plasma, gastrointestinal tract, hematopoietic organs and liver by HPLC-MS/MS. Muscle samples were taken at 0.25, 0.5, 1, 3, 7, 14 and 28 days post dose, whereas plasma, gastrointestinal tract, hematopoietic organs and liver concentrations were measured at 1, 3, 7, 14 and 28 days post-dosing. The kinetic profiles of $C_{max}$, $T_{max}$, $T_{1/2}$ of CDX were analyzed by fitting to a non-compartmental model with PKSolver program. The following pharmacokinetic parameters were obtained with oral administration of 45 and 225 mg/kg at 13 and $22^{\circ}C$ in muscle, plasma, gastrointestinal tract, hematopoietic organs and liver, respectively: $C_{max}$ (maximum tissue concentration)=$985.98-5,032.86{\mu}g/kg$, $5,670.99-38,922.23{\mu}g/l$, $2,457.27-10,192.78{\mu}g/kg$, $886.04-3,070.87{\mu}g/kg$ and $1,188.15-3,814.33{\mu}g/kg$; $T_{max}$ (time for maximum concentration)= every 1 day; $MRT_{0-{\infty}}$ (mean residence time)= 1.51-4.74, 2.12-3.06, 4.25-13.18, 1.37-18.66 and 1.78-29.76 days; $T_{1/2}$ (half-life)= 1.08-3.47, 1.14-5.42, 3.56-10.99, 1.17-14.93 and 1.25-28.55 days.