Fractionation of the ethanolic extract of the stem bark of Morus yunanensis resulted in the isolation of a new Diels-Alder type adduct and two new flavones, named yunanensin A (1), yunanensol A (2) and yunanensol B (3), respectively, together with a known flavone (4). Their structures were determined on the basis of spectroscopic analysis and chemical methods. Among them, compound 1 showed moderate antioxidant and significant cytotoxic activities, and compound 2 showed potent anti-inflammatory activity.