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Despite its beneficial role in host defense mechanisms, excessive nitric oxide (NO) production by activated macrophages has been implicated in several inflammatory diseases. To clarify the mechanisms of the anti-inflammatory activities of Sargassum micracanthum, we evaluated whether extracts of S. micracanthum could modulate the production of NO by activated macrophages. S. micracanthum were extracted with 80% EtOH. The extract was then successively partitioned with hexane, CH 2 Cl 2 , EtOAc, BuOH, and water. The results indicate that the hexane and CH2Cl2 fractions of S. micracanthum extract were effective inhibitors of LPS-induced NO and prostaglandin E2 (PGE2) production in RAW 264.7 cells. The inhibitory effects of the hexane and CH2Cl2 fractions of S. micracanthum were accompanied by dosedependent decreases in the production of iNOS and COX-2 proteins and iNOS and COX-2 mRNA expression. To test the inhibitory effects of S. micracanthum fractions on other cytokines, we also performed ELISA and RT-PCR assays for TNF- , IL-1s, and IL-6 in LPSstimulated RAW 264.7 macrophage cells. In these assays, the hexane and CH2Cl2 fractions of S. micracanthum produced dose-dependent decreases in the production and mRNA expression of TNF- , IL-1s, and IL-6. To test the potential application of S. micracanthum extract as a cosmetic material, we also performed MTT assays on human dermal fibroblast cells, as well as primary skin irritation tests. In these assays, S. micracanthum extracts did not induce any adverse reactions. Based on these results, we suggest that S. micracanthum extracts may be considered potential anti-inflammatory candidates for topical application.