Horseradish roots were cut off into chips and they were dehydrated under airing at low temperature or freeze drying. Volatile sulfur compounds in the hydrolysates of fresh and dried materials were investigated by gas chromatography equipped with FPD.(1) The following 7 isothiocyanates were detected in the hydrolysates of experimental materials: iso-propyl, sec-butyl, allyl, 3- butenyl, 4-pentenyl, 3-methylthiopropyl, and β-phenethyl isothiocyanates. Three unknown volatile sulfur compounds were also detected. In fresh materials the peak area (%) of allyl isothiocyanate to that of internal standard, phenyl isothiocyanate, was the highest, followed by β-phenethyl and 3-butenyl isothiocyanates. (2) By drying thematerial the peak areas (%) of sec-butyl and 3-butenyl isothiocyanates increased, whereas the peak area (%) of β-phenethyl isothiocyanate fairly decreased.