A glycosylation reaction was performed using a combination of thioglycoside and glycosyl sulfoxide, which were prepared with odorless p-octyloxybenzenethiol, as a glycosyl donor and an acceptor, respectively. Promising results were obtained when p-octyloxylphenyl N-phthaloyl-D-thio-glucosaminide was activated with N-iodosuccinimide (NIS) and triflic acid (TfOH) for glycosylation of the hydroxyl group of the C-6 position of derivatives of D-glucosyl sulfoxide. Successive reduction of the resulting disaccharyl sulfoxides provided the corresponding thioglycosides, which could be used as the glycosyl donors in another glycosylation reaction to afford trisaccharides in good yield. The present method would be useful for the block synthesis of glycosyl donors in the total synthesis of blanched oligosaccharides, especially when N-acetylglucosamines are presented at the non-reducing ends.