We have previously shown that royal jelly (RJ) promoted collagen production by skin fibroblasts in the presence of ascorbic acid-2-O-alpha-glucoside (AA-2G). In this study, we purified the honeybee RJ-derived collagen production-promoting factor (HBRJ-CPF) from an alkali-solubilized fraction of RJ by C18 reverse-phase column chromatography. The elution profile by the C18 column chromatography and the molecular mass of the purified HBRJ-CPF material coincided with those of 10-hydroxy-2-decenoic acid (10H2DA). We then examined the collagen productionpromoting activities of several commercially available fatty acids contained in RJ. We found that 10H2DA and 10-hydroxydecanoic acid increased the collagen production in a dose-dependent manner. Furthermore, 10H2DA induced the fibroblast cell line, NHDF, to produce transforming growth factor-1 (TGF-1) which is an important factor for collagen production. As expected, the collagen production-promoting activity of 10H2DA was neutralized by the anti-TGF-1 antibody. These result suggest that HBRJ-CPF identified as 10H2DA promoted the collagen production of AA-2G-treated fibroblasts by inducing TGF-1 production.