A pharmaceutical composition useful as acetylcholinesterase inhibitors. The present invention relates to pharmaceutical composition comprising the naturally occurring compounds selected from (.+-.) Marmesin, Columbianetin, Dihydroxanthyletin and substituted coumarin derivatives of 7-allyloxy coumarin, 7-benzyloxy coumarin, 7-methoxy coumarin, 7-acetyloxy coumarin, 4-methyl-7-hydroxy coumarin and 4-methyl-7-acetyloxy coumarin. The said compositions posses a high degree of acetylcholinesterase inhibitory (AChE) property.