A fast, simple and accurate method for determining the concentration of amoxicillin (AMX), a b-lactam antibiotic, in rat plasma has been developed. This method involves a deproteinization procedure by methanol with 0.2% perchloric acid and reversed-phase high-performance liquid chromatography with ultraviolet detection at 220 nm. Regression analysis showed that the method was linear over the standard curve range from 0.1 to 160 µg/ml.  The inter-day precision and accuracy values between the ranges were 8.1% or better and 94.4 – 105.0%, respectively. The newly developed method has been applied in the analysis of plasma samples in pharmacokinetic studies in rats. Pharmacokinetics of AMX after intravenous administration to rats was studied at doses of 3.5, 7, 15, and 25 mg/kg.  The AUC values were 3.13 ± 0.28 (mean ± SE of 4 rats), 6.98 ± 0.51, 15.19 ± 2.06 and 27.46 ± 3.85 μg h/ml, respectively. A linear relationship between the doses and AUC values, y=1.1256x – 1.0210, r=0.999, was observed. The MRT values at the doses were 0.55 ± 0.09, 0.62 ± 0.02, 0.55 ± 0.05 and 0.52 ± 0.02 h. The CL values were 1144.03 ± 93.41, 1017.12 ± 65.05, 1068.23 ± 197.72 and 963.74 ± 130.79 (ml/h/kg). The Vdss were 609.19 ± 74.30, 629.43 ± 33.25, 568.23 ± 58.64, and 493.58 ± 51.43 (ml/kg). The MRT, CL, and Vdss were constant among the doses. It was found from these results that AMX shows linear pharmacokinetics in rats after intravenous administration at doses from 3.5 to 25 mg/kg.