Provided is a mucosal immunostimulator that comprises, as an active ingredient, at least one member selected from a saturated fatty acid represented by general formula (1) and a salt thereof: R-COOH (1) [in general formula (1), R represents a C7-11 alkyl group substituted by one hydroxy group].本發明提供一種黏膜免疫調節劑,其含有選自由下述通式(1)所表示之飽和脂肪酸及其鹽所組成之群中之至少1種作為有效成分;R-COOH (1)[通式(1)中,R表示經1個羥基取代之碳數7~11之烷基]。