Abstract: The weight of casein protein fibers with different protein contents during moisture absorption & moisture evaporation was measured under standard atmosphere conditions.After analyzing its moisture absorption & moisture evaporation properties,plotted the relative curve,and made the regression equation of the moisture regain to time and the regress equation of the rate of moisture absorption & moisture evaporation.The results indicated that the time needed for reaching balance of moisture absorption & moisture evaporation is similar to the data shown in the curve.Higher the protein content in casein protein fiber,better the moisture absorption of the fiber.The time needed for reaching the balance of moisture absorption of casein protein fiber is shorter than that of moisture evaporation.