The structures of new acetylcholinesterase inhibitors, arisugacins A and B, were elucidated by NMR study. Arisugacins have a (4aR,6aR,12aS,12bS)-4a,6,6a,12,12a, 12b-hexahydro-4a,12a-dihydroxy-4,4,6a,12b-tetramethyl-4H,11H -naphtho[2,1-b] pyrano[3,4-e]pyran-1,11(5H)-dione moiety in common and 3,4-dimethoxyphenyl or 4-methoxyphenyl residues are attached to C-9 of the moiety.