Five new isoprenylated flavonoids, notabilisins A-E (1-5), and two known Diels-Alder adducts (6 and 7), were isolated from the twigs of Morus notabilis. Compounds 4 and 5 possess two novel pyran rings, which may be biogenetically derived from 3. Compounds 1 and 3 significantly promoted adipogenesis, characterized by increased lipid droplet and triglyceride content in 3T3L1 cells, and induced up-regulation of the expression of adipocyte-specific genes, aP2 and GLUT4.