As a tool to understand the role of mucins in the infection of respiratory viruses, we established cell lines stably expressing inactive mutants of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 3 (GALNT3), which initiates O-glycosylation of mucins. We introduced single amino acid mutations into the regions essential for the enzyme activity of GALNT3 using the expression plasmid of human GALNT3 and transfected the mutant constructs into a human bronchial epithelial cell line, BEAS-2B. We showed that although the mutants of GALNT3 exhibit an authentic localization at the Golgi apparatus, the glycosylation pattern of the expressing cell lines appeared to be different from that of the cells expressing wild-type GALNT3. These results suggested that the established cell lines express inactive forms of GALNT3 and might be useful in investigation of the significance of O-glycosylation of mucins in respiratory virus infections.