A pentacyclic triterpenoid compound was isolated from the ethyl acetate extract of sedum (Sedum sarmentosum) and identified as D-friedoolean-13-en-3-one (taraxerone) by GC-MS and crystallographic analysis. The extraction yield of taraxerone was $74.12{pm}0.57$ mg/kg sedum (dry weight). The $IC_{50}$ values of taraxerone were $102.34{pm}1.53{mu}M$ and $1,763.81{pm}12.63{mu}M/mL$ (Trolox equivalent) by the DPPH and ferric reducing ability of plasma (FRAP) assays, respectively. Taraxerone exhibited comparable antioxidant capacities with butylated hydroxytoluene (BHT) by the DPPH (p=0.117) and FRAP (p=0.179) assays. The production of inducible nitric oxide in lipopolysaccharide-stimulated murine macrophage was inhibited by taraxerone ($IC_{50}=38.49{pm}3.77{mu}M$) via downregulation of inducible nitric oxide synthase (iNOS) expression at the transcriptional level. The inhibitory effect of taraxerone on nitric oxide generation was significantly more effective than that of caffeic acid and/or gallic acid.