Piperine was reported to have a potential central nervous system (CNS) depressant activity in mice. In order to search a more active and less toxic compound than piperine and to elucidate the active group of piperine, the aromatic amides (10 compeunds) and aromatic esters (10 cempounds) of 3, 4-methylenedioxycinnamic acid were synthesized and evaluated on CNS depressant activity in comparison with piperine. The pharmacological tests conducted are as follows; (1) Acute, toxicity, (2) Antagonism against strychnine induced conduced convulsion, (3) Antagonism against maximal electrobhock seizure, (4) Rotarod test, (5) Potentiation of hexobarbital sleeping time. It was observed that 3, 4-methylendioxycinanamic acid derivatives were less toxic than piperine, and showed no significant CNS depressant activities. These facts indicate that the piperoyl group might be concerned with the pharmacological activity of piperine.