Five kinds of coumarin compounds were successfully purified from Angelica gigas Nakai by using recyclingpreparative HPLC and identified as decursin (1), decursinol angelate (2), 7-demethylsuberosine (3), marmesin (4), and decursinol (5) by NMR analyses. None of the purified compounds in ethanol showed DPPH radical scavenging activity, while the A. gigas extract (AGNEX) displayed a significant level of activity. Interestingly, compounds 3 in phosphate buffered saline (PBS) showed good $ABTS^+$ radical scavenging activity ($IC_{50}=8.1{mu}g$/mL) as did compounds 4 and 5. The anti-inflammatory activities of the purified compounds were evaluated and compared using the NO concentration assay and western blot analysis on LPS-stimulated RAW 264.7 cells. NO production was significantly suppressed by all the compounds in a dose-dependent manner among which compounds 1, 2, and 3 showed very good activities with $IC_{50}$ values of 7.4, 6.5, and $7.6{mu}g$/mL, respectively. Treatment with compounds 1-5 effectively suppressed the expression levels of iNOS, IL-1$eta$, and COX-2, which are responsible for promoting the inflammatory process. Thus, the ethanol extract and coumarin compounds of A. gigas Nakai hold promise for use as potential anti-inflammatory agents.