Abstract: A pair of primers was designed to clone IL-2 gene according to the codon bias principle and the recombinant expressed vector pPIC9k-IL-2 was constructed. The recombinant plasmid was transformed into P. pastoris GS115 by electroporation, the positive recombinant strains was screened with different G418 concentration and induced with methanol. The result showed that IL-2 gene was integrated with chromosome of P. pastoris by PCR identification. The expressed product had a molecular weight of 16 and 20 kD bands by SDS-PAGE analysis. The result of deglycosylation analysis indicated that the protein was glycosylated moderately. The protein was purified with sephadex column and had a bioactivity of lymphocyte proliferation. The Western blotting analysis showed that target protein had immunological activity. P. pastoris expressed system is an efficient way of production of pIL-2, the expressed product had a good bioactivity.