Objective The competent Pichia pastoris was transformed by the recombinant plasmid pPIC9k-HSA-IFNα-2b which was cut with restriction endonuclease  SalI through electroporation. Then the target protein was induced to express by methanol. We made the preliminarily study on   the expression conditions and the genetic stability of the positive  transformants.   Methods   The  integrate   gene  pPIC9k-HSA-IFNα-2b  was identified   by   digesting   with   restrictive   endonuclease   EcoRI/BamHI.   Then   the recombinant plasmid pPIC9k-HSA-IFNα-2b was digested with restrictive endonuclease SalI. The lined recombinant plasmid DNA was transformed into the competent Pichia Pastoris SMD1168 through electroporation, then the Pichia Pastoris integrants was analyzed  with  PCR  method  and  screened  for  the  Mut  phenotype  of positive transformants on MM and MD plate. The positive transformants were induced to express by methanol and the expressed supernatant was identified by Western-Blot. The expression level of positive transformants was identified by ELISA and the level of its G418 resistence was measured on YPD-G418 plate. The anti-virus activity of the expressed rhHSA-IFNα-2b was measuredby Wish -VSV system. We studied the effect of methanol concentration and OD_(600) value on the expression level of the positive transformants. Finally, we analyzed the genetic stability of the positive transformants. Results    The lined recombinant plasmid DNA successfully transformed into the competent Pichia pastoris  SMD1168 and integrated into SMD1168 chromosome through electroporation and the target protein was expressed in positive transformants and secreted into medium, which was induced by methanol. The expression level reaches as high as 300mg/L in medium through ELISA and the specific activity was