A new sesterterpenetriol named kobiin and three new 2-furanones named kobifuranones A, B, and C were isolated from an Ascomycete, Gelasinospora kobi. Kobiin, the main immunosuppressive principle of this fungus, possesses a bicyclic skeleton of five- and fifteen-membered rings. Kobifuranones A, B, and C were supposed to be metabolites formed from a common intermediate biosynthesized through the acetate-malonate pathway. The immunosuppressive activity of kobiin and kobifuranones A, B, and C was evaluated in a system of mouse spleen lymphocytes stimulated to proliferate with concanavalin A and lipopolysaccharide.