Abstract: Four kinds of casein grafted acrylonitrile fibers with different casein feed ratioes were studied. Through analyzing and comparing the morphological structure, chemical composition, component content, the basic mechanical properties, and the frictional, hygroscopic and dyeing properties, the influence of different casein content on the performance of grafted fibers were investigated. The results showed that the grafted casein fiber is a mixture of three different things, which includes Casein-g-AN, PAN and casein. With the increase of casein content, the strength of the fiber is enhanced in some degree, and the properties of hygroscopicity and dyeing are enhanced significantly. But the formability was weakened with exorbitant casein content, lowering the fiber quality. Finally, some constructive suggestions for exploiting and making use of this kind of casein grafted acrylonitrile fibers are put forward.