The recombinant human interferon alpha 2α(rhIFN-a2a), expressed in Saccharomyrces cerevisiae, was purified from insoluble aggregates. The inclusion body of rhIFN-α was solubilized by guanidine salt in the presence of disulfide reducing agent. The refolding of denatured rhIFN-α2a was achieved by simple dilution. The authentic interferon alpha, which has two correctly matched disulfide bonds, was seperated from incompletely oxidized IFN-α and dimeric IFN-αa, by use of a CM-Sepharose column, followed by size exclusion columns at two different pH conditions. The purified protein has been subjected to detailed physicochemical characterization including sequence determination. Unlike other rhIFN-α2a from E. coli reported, the rhIFN-α2a from S. cereuisioe has no methionine residue at its N-terminus originating from the start codon, ATG. The pI of the protein was determined to be 6.05 with a single band in the pI gel, which demonstrated that the purified rhIFN-α was homogeneous. The structural study using circular dichroism showed that the protein retains its three dimensional structure in the wide range of pH conditions between pH 3 and 9, and only minor structural deformation was observed at pH 1.0.