We investigated the active components responsible for the anti-allergic effect of Hypsizigus marmoreus on an oxazolone-induced type IV allergy in male ICR mice. Following both an oral administration at a dose of 250 mg/kg body weight and percutaneous administration at 0.10 mg/ear, significant anti-allergic activities were found in the 80% ethanolsoluble fraction (Fr. 1), and the low molecular weight fraction (Fr. 2, below a molecular weight of ca. 12000; Fr. 4, below ca. 3000) prepared from Fr. 1. These fractions included ergosterol, mannitol, and trehalose as antioxidants and/or anti-inflammatory components. The anti-allergic activities of these compounds and methionine were equal to or weaker than those of the fractions. Therefore, the molecular weights of the major active components in Hypsizigus marmoreus are thought to be less than ca. 3000, though ergosterol, mannitol, trehalose, and methionine would not be the main active components.