Trehalase (EC 3.2.1.28), which specifically hydrolyzes trehalose (1 -a-D-glucopyranosyl-a-D-glucopyranoside) to two glucose moieties, is widely distributed in animals, plants, microorganisms, and insects. The substrate trehalose, ubiquitously found in insects, is the principal blood sugar in many insects. Trehalose, found in hemolymphs of insects, is used to support various energy-requiring functions, such as insect flight.1>2) The other biological functions of trehalose or trehalase are also reported for germination of ascospores in fungi3~6) and glucose transport in mammalian kidney or intestine. 7) In the course of our screening of specific and potent inhibitors of trehalase, we have succeeded in isolating a microorganism producing a potent and specific inhibitor of trehalase. As described below, the inhibitor was different from the reported trehalase inhibitors, such as proteinaceous inhibitor,8'9) S-GI (deoxynojirimycin),10) validamycins,11'12) and validoxylamine.13) Therefore, the trehalase inhibitor was named "trehalostatin" for its specific inhibitory spectrum.