This study investigates the change in chemical and crystalline structure of pulp samples during alkali sulfite process at different cooking temperatures and time, TAPPI and SCAN standard test methods and X-ray diffraction and FT-IR spectroscopy were used. It was shown that the crystalline structure of cellulose in hemp (Cannabis sativa L.) bast fibers was very strong and stable. Crystallinity of alkali sulfite pulp samples obtained from processing at 140 up to 180 degrees C increased, but then decreased at 200 degrees C. The crystallite size of cellulose in alkali sulfite pulp samples increased with cooking temperature. The crystalline allomorph of cellulose in alkali sulfite pulp samples obtained at 200 degrees C changed from monoclinic structure to triclinic structure. Crystalline structure of cellulose in alkali sulfite pulp samples was little affected by changing cooking time. It was concluded that cooking temperature during alkaline sulfite pulping process had more effect on carbohydrate components and crystalline structure of pulp samples than cooking time. (c) 2006 Elsevier Ltd. All rights reserved.