ABSTRACTViscosity of irradiated black and white peppers decreased depending upon dosage, and viscosity was not lowered by other decontamination treatments such as super‐heated steam or fumigation with ethylene oxide gas. Viscosity values of unirradiated pepper varied with the lot and harvesting locality. A normalized parameter, viscosity/starch amount, of a 10% suspension of unirradiated pepper was always higher than 190 mPa.s/g of starch and that of irradiated pepper (5 kGy) was always lower than 180 mPa.s/g of starch, irrespective of lot and harvesting locality.