Isoegomaketone (IK) is an essential oil component of Perilla frutescens (L.) Britt., and there have been no studies investigating its biological activities. We found that IK inhibits lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophages, and moreover, when IK was injected into animals prior to LPS administration, NO serum levels decreased in a dose-dependent manner. These results indicate that IK possesses anti-inflammatory activity both in vitro and in vivo. IK suppressed the phosphorylation of STAT-1 and the production of IFN-beta. Treatment with IK also inhibited the activation of NF-kappaB and activator protein-1, but more IK was required for inhibition than for STAT-1 inhibition, indicating that downregulation of inducible nitric oxide synthase gene expression by IK is mainly attributed to the blockade of STAT-1 activation. Furthermore, IK also induced the expression of heme oxygenase-1 (HO-1) through the activation of nuclear factor E2-related factor 2. Treatment with SnPP, a selective inhibitor of HO-1, reversed the IK-induced suppression of STAT-1 phosphorylation and NO production. Taken together, IK isolated from P. frutescens inhibits NO production in LPS-treated RAW 264.7 macrophages through simultaneous induction of HO-1 and inhibition of the IFN-beta-STAT-1 pathway.