The present invention generally relates to new process for the preparation of iron (III) casein N-acetyl-aspartylated complexes. The product obtainable according to the method of the present invention may be safely used to the general population or animals in the therapy of iron deficiency. The process of the invention includes the steps of:(a) reaction of casein with N-acetyl-L-aspartyl chloride, to form N-acetyl-L-aspartylated casein,(b) subsequent reaction of the N-acetyl-L-aspartylated casein with ferric chloride； and(c) obtaining the iron (III) complex with N-acetyl-L-aspartylated casein.
