Royal jelly is a food for queen and larvae honeybees. 10-Hydroxy-trans-2-decenoic acid (10H2DA; "royal jelly acid") is the principal lipid component in royal jelly. Several pharmacological activities of 10H2DA have been reported: anti-tumor, anti-biotic, immunomodulatory, estrogenic and neurogenic. We recently revealed an inhibitory effect of 10H2DA in innate immune signals. Despite appreciable advances in studies on innate immune signals after the identification of Toll-like receptors as innate immune receptors, few studies have reported the effect of 10H2DA on innate immune signals. In this review, we focus on recent advances in the evaluation of the biological activities of 10H2DA (especially immunomodulatory activities). We also discuss the molecular mechanisms underpinning these biological activities, which could lead to new therapeutic targets for the treatment of immune disorders.