β-1,3-galactosyltransferase-1 (β3GalT-1) is the key enzyme to form the type 1 chain structure. Northern blot analysis indicated that β3GalT-1 was expressed predominantly in the brain. In the present study, it was revealed that the gene expression of β3GalT-1 in mouse brain was developmentally decreased. High expression levels of β3GalT-1 were found in cerebral cortex and hippocampus in both newborn and adult mice, while in cerebellum, the expression levels decreased markedly during development. In situ hybridization revealed that the absence of expression in cerebellar granual cell layers contributed to the main loss of β3GalT-1 expression in adult mouse cerebellum. Moreover, the decreased levels of β3GalT-1could affect the synthesis of type 1 chain oligosaccharides, as revealed by immunohistochemistry analysis. © 2003 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.