The present invention relates to a composition for the prevention or treatment of arthritis, the composition containing a Sargassum serratifolium extract as an active ingredient. The extract of Sargassum serratifolium according to the present invention has an excellent activity to reduce or inhibit the activity of IL-1β, IL-6, or TNF-α, which is an inflammatory cytokine, and has an excellent effect alleviating arthritis in an arthritis animal model so that it can be usefully used as a composition for treating arthritis. In addition, there is no cytotoxicity, and toxicity to the drug and side effects are avoided so that it can be safely used even for long-term use, and it is stable in the body.
