According to the invention, there is provided a novel 3,4-dihydroxyhydrocinnamic acid derivative, designated DHH105, having blood glucose lowering effects in vivo as a result of the enhancement of glucose transport mediated by the increase of insulin receptor signaling.This invention thus relates to a 3,4-dihydroxyhydrocinnamic acid derivative useful as an anti-diabetic agent, represented by the following formula I: ##STR00001## or pharmaceutically acceptable salts thereof, to a method for preparing the compound, and to a composition for treating diabetes comprising the same as an active ingredient.