A reversed-phase liquid chromatographic method for decursin and decursinol angel ate of Angelicae gigantis Radix, an important crude drug in Korean traditional medicine, was developed and validated. Decursin and decursinol angel ate, the structure isomer (pyranocoumarin) each other, are the main organic constituents in Angelicae gigantis Radix. This method was developed using a RP-18 column, UV detector at 280 ㎚ and 50% acetonitrile solution containing 0.01 M sodium dodecyl sulfate and 25mM sodium dihydrogen phosphate (pH 5.0) as the mobile phase. Various validation parameters were included and evaluated satisfactorily. Linearity was established in range 2-75 ㎎/ml of decursin and decursinol angel ate (correlation coefficient = 0.9997 and 0.9995, respectively). This analytical method showed good accuracy (98.1% and 99.5%, respectively). Precision (repeatability) revealed a relative standard deviation value of 1.71% (decursin) and 3.19% (decursinol angelate). For intermediate precision measure the considered variables were equipment and days. A robustness test showing the influence of deferent counter-ion concentration in mobile phase was also performed.