Protein A and protein L are bacterial cell wall proteins of importance in pathogenesis which have different crystal structures and bind different sites of host immunoglobulin (Ig). A pair of primers containing SacⅠ sequence were synthesized to amplify A,B,C,D domain of protein A and B3 domain of protein L by PCR respectively. After digestion with restriction enzyme SacⅠ , these PCR prepared Ig-binding domains were ligated randomly with each other to come into being a combinatorial molecular library. The library was displayed on phage surface by cloning into SacⅠ site of phagemid pCANTAB5S. The capacity of the phage library were calculated as 3.4×107 clones,and the titer was 6.2×1010 TU/ml. The sequence analysis showed that the displayed DNA fragments in the library comprise of various Ig-binding domains ligated in random. After three or four rounds affinity selection with human Ig, 36 positive clones were sequenced at random to analyze structure of the recombinant molecules. The sequence analysis showed 3 kinds of new molecular structures existed in the selected molecules which were totally different from its natural molecules. The characteristic structure of (MDPL-MDPA)n which consists of the repetition of mono-domain of protein A(MDPA) and mono-domain of protein L (MDPL) existed predominantly in 32 of 36 positive clones. The effort to proceed molecular evolution study of Ig-binding domains combinatorial molecular library by phage display not only provides potent approach for research involved in the relationship between structure and function of Ig-binding molecules, but also a basis for Ig-binding molecules rebuilding.