A high performance liquid chromatographic (HPLC) method for the simultaneous determination of marker constituents, paeoniflorin and glycyrrhizin was established for the quality control of traditional herbal medicinal preparation, Sayuk-san (SYS). Separation and quantification were successfully achieved with a Waters XTerra RP18 column ($5{mu}m$, $4.6mm;I.D.{ imes}150mm$) by gradient elution of a mixture of acetonitrile and water containing 0.03% phosphoric acid (pH 2.03) at a flow rate of 1.0 mL/min. The diode-array UV/vis detector (DAD) was used for the detection and the wavelength for quantification was set at 230 nm. The presence of paeoniflorin and glycyrrhizin in this decoction was ascertained by retention time, spiking with each authentic standard and UV spectrum. All two compounds showed good linearity ($r^2$>0.996) in a relatively wide concentration ranges. The R.S.D. for intra-day and inter-day precision was less than 7.3% and the limits of detection (LOD) were less than 55.7 ng. The mean recovery of each compound was $102.3{sim}111.1%$ with R.S.D. values less than 4.6%. This method was successfully applied to the determination of contents of paeoniflorin and glycyrrhizin in three commercial products of SYS. These results suggest that the developed HPLC method is simple, effective and could be readily utilized as a quality control method for commercial SYS products.