Abstract: Preparation technology of anhydrous cerium chloride from cerium chloride heptahydrate (CeCl<SUB>3</SUB>·7H<SUB>2</SUB>O) by vacuum dehydration method was researched.Theoretical basis of dehydration process was introduced,and effects of mixture ratio of raw materials,dehydration temperature,dehydration time,and vacuum degree on purity of anhydrous cerium chloride were investigated.Based on the single factor study,optimum conditions of dehydration were obtained as follows:dosage of ammonium chloride is 30% (mass fraction of ammonium chloride accounts for the mixture of ammonium chloride and&nbsp;cerium chloride heptahydrate),vacuum degree is 0.04 MPa,constitution water removal temperature is 160 ℃,and vacuum dehydration time is 200 min.Purity of anhydrous cerium chloride could excess 93%under optimum conditions.