A series of semi-rigid analogs of phenethylamine was prepared as fixed transoid and cisoid analogs of mebeverine, and tested for spasmolytic activity in vitro. The fixed transoid analogs were more potent than the corresponding cisoid analogs. In this series, tetrahydro-2-napthylamine derivative (2a) which is presumed to take transoid conformation had the most potent activity, and tetrahydroisoquinoline derivatives (2g and 2h) which are presumed to take typical cisoid conformations were less active. These results suggested that the phenethylamine moiety of mebeverine takes the transoid conformation for the manifestation of the spasmolytic activity.