Abstract: A rapid and sensitive column-switching high performance liquid chromatographicprocedures was described for determination of captopril in plasma and urine, ρ-Bromophenacylbromide, a derivatizing reagent, was added to the plasma and urine samples to form an adduct whichshowed ultraviolet absorbing properties. After that, the urine sample was injected directively and forplasma the protein was removed with 6% of perchloride before injection. The column-switching sys-tem was equipped with a pre-column of 5 cm×0.5 em ID, packed with μBoundapak C₁₈,37～50μm,and an analytical column of 15 cm×0. 5 cm ID, packed with YWG-C₁₈,10μm. After washing outthe imputes from pre-column with 0.2% acetic acid the retained substances were eluted into analyticalcolumn with acetonitrile-water-acetic acid(35:65:0.4). Captopril was detected at 260 nm. Themethod was linear within 20～1000 rig/ml for plasma and 10～200 μg/ml for urine. The recovery av-eraged 103. 2% and 99.5% for plasma and urine, respectively. The coefficient variations were all le-ss than 10%.