An ultra-performance liquid chromatography-electrospray ionization-mass spectrometer (UPLC-ESI-MS) method was established for the simultaneous quantification of eighteen marker compounds in traditional Korean formula, Cheonwangbosimdan (CWBSD). In addition, we evaluated the antioxidant effects of CWBSD. Eighteen marker components were separated on a UPLC BEH C18 analytical column (2.1×100 mm, 1.7 μm) and kept at 45 o C by gradient elution with 0.1% (v/ v) formic acid in water and acetonitrile as mobile phase. The flow rate was 0.3 mL/min and the injection volume was 2.0 μL. The antioxidant activities of CWBSD were assessed by measuring free radical scavenging activities on 2,2``-azinobis-3-ethylbenzothiazoline- 6-sulfonic acid (ABTS) and 1-1-diphenyl-2-picrylhydrazyl (DPPH). The calibration curves of all analytes showed good linearity (correlation coefficient ≥0.9937) within the test ranges. The limits of detection and quantification for the 18 marker compounds were 0.01-4.71 ng/mL and 0.03-14.13 ng/mL, respectively. The contents of the 18 compounds in CWBSD extract ranged from none to 1701.00 μg/g. The CWBSD showed the radical scavenging activity in a dose-dependent manner. The concentration required for 50% reduction (RC50) against ABTS and DPPH radicals were 149.42 μg/mL and 339.24 μg/mL.