Glucosylceramide synthase-IN-2 (compound T-690) is a potent, brain-penetrant and orally active glucosylceramide synthase (GCS) inhibitor with IC50s of 15 nM and 190 nM for human GCS and mouse GCS, respectively.Glucosylceramide synthase-IN-2 exhibits noncompetitive type inhibition with C8-ceramide and UDP-glucose.Glucosylceramide synthase-IN-2 can be used for Gaucher's disease research.