The syntheses of alkyldisiloxanes containing sugar moiety with various alkyl chain length were investigated, in order to develop a silicone-based transdermal penetration enhancer which was expected to show a low irritation to the skin. 1-Alkyl-3-beta-D-glucopyranosyl-1,1,3,3-tetramethyldisiloxanes (Glc-SiCs) were prepared by two-step hydrosilylations of 1-alkene and 1-allyl-beta-D-glucose tetraacetate with 1,1,3,3-tetramethyldisiloxane in the presence of bis(benzonitrile)platinum dichloride as the catalyst, followed by hydrolysis of the acetyl groups with sodium methoxide. The enhancing effect of Glc-SiCs on the percutaneous drug penetration was evaluated by in vitro experiments using a two-chamber diffusion cell. Antipyrine (ANP) and indomethacin (IND) were used as hydrophilic and hydrophobic model drugs, respectively, and the amount of drug permeating through the rat abdominal skin with or without Glc-SiCs was estimated by HPLC. As a result, Glc-SiCs exhibited a enhancing effect on the permeation of both drugs through the skin, which was influenced by the alkyl chain length of Glc-SiCs. In addition, it was suggested that a suitable balance of polarity would be necessary to appear the high enhancing effect, where Glc-SiCs with octyl and decyl groups exhibited the highest enhancing effect. From the determination of kinetic parameters in the drug permeation, it was also found that this enhancing effect was due to the increase of both partition and diffusion coefficients of drug permeation through the skin. By experiments to determine the amount of cholesterol extracted from the skin, the defatting effect would be one of the functions of Glc-SiCs which resulted in the high enhancing activity. Furthermore, according to the Draize test, it was confirmed that Glc-SiCs showed a low irritation to the skin.