6,6'-Dideoxy-6,6'-diisothiocyanato-alpha,alpha'-trehalose (4), 6-deoxy-6-isothiocyanato-alpha-D-fructo-furanose beta-D-fructopyranose 1,2':2,1'-dianhydride (11), 6,6'-dideoxy-6,6'-diisothiocyanatosucrose (16), and per(6-deoxy-6-isothiocyanato)-cyclomaltohexaose (23), -cyclomaltoheptaose (27), and -cyclomaltooctaose (31) have been prepared in high yield by reaction of the corresponding amino sugars with thiophosgene. In the absence of base, all isothiocyanates were stable and could be stored and acetylated without decomposition. In the presence of triethylamine, 6,6'-dideoxy-6,6'-diisothiocyanato-alpha,alpha'-trehalose underwent intramolecular cyclisation involving HO-4 to give the corresponding bis(cyclic thiocarbamate). The product of cyclisation at a single glucopyranosyl unit was obtained in the treatment of the above diisothiocyanate with mixed (H+, HO-) ion-exchange resin. Under identical reaction conditions, 6,6'-dideoxy-6,6'-diisothiocyanatosucrose yielded exclusively the product of intramolecular cyclisation at the D-glucopyranosyl moiety, while derivatives of alpha-D-fructofuranose beta-D-fructopyranose 1,2':2,1'-dianhydride and cyclomaltooligosaccharides remained unchanged.