Abstract: The present invention relates to novel huperzine A derivatives of formula (II), wherein Y is ##STR1## or R" and Y together form .dbd.CH; R is (C.sub.1 -C.sub.5) alkyl, ##STR2## wherein n is 0 or 1, X is H, (C.sub.1 -C.sub.5) alkyl; (C.sub.1 -C.sub.5) alkyloxy; nitro, halogen, carboxy, alkyloxycarbonyl, hydroxymethyl, hydroxy, amino substituted by bis-(C.sub.1 -C.sub.5) alkyl; --(CH.sub.2).sub.m COOZ, wherein m=0-5, Z is H or (C.sub.1 -C.sub.5) alkyl; --CH.dbd.CH--G, wherein G is phenyl, furanyl, carboxy, alkyloxycarbonyl; and dihydro- or tetrahydro-pyridyl substituted by (C.sub.1 -C.sub.5) alkyl at the nitrogen atom; R' is H, (C.sub.1 -C.sub.5) alkyl, pyridoyl, benzoyl substituted by (C.sub.1 -C.sub.5) alkyloxy; R" is H or (C.sub.1 -C.sub.5) alkyl; processes for their use as acetylcholinesterase inhibitor.