10-Hydroxydecanoic acid (10-HDA) is a saturated fatty acid of hydroxy-trans-2-decenoic acid (10H2DA). Its molecule has two functional groups (-OH and -COOH). It has been reported to prevent the lipopolysaccharide-induced NO production in murine macrophages. 10-HDA has been extracted from royal jelly obtained from honeybees (Apis mellifera) and exhibits estrogenic action. Its polymerization with the polyethylene glycol-modified lipase in a transparent benzene solution has been reported to proceed by the formation of ester linkage.