Glutaminase(EC 3.5.1.2) was applied in the present work to treat casein for deamidation and hydrolysis to a limited reaction extent.SDS-PAGE and size exclusion chromatography analysis were used to evaluate the degradation of casein.Some deamidated casein products with lower degree of deamidation were prepared with reaction conditions of casein concentration of 5 %(w/v),glutaminase addition level of 400 U/kg casein,reaction temperature of 37 ℃ and reaction time were 6,12 and 24 h,respectively.Three deamidated casein products prepared had the degree of deamidation of 2.8%,5.8% and 8.5 %,or degree of hydrolysis of 2.5%,3.4% and 4.9 %,respectively,were prepared.The iron or calcium(Ⅱ) chelating activities of three deamidated caseind products were analyzed.The results indicated that the iron or calcium(Ⅱ) chelating activities of three deamidated casein products were higher than that of casein,and would be enhanced as degree of deamidation increased.