To facilitate the mutation of Milano site, the whole proapo AI_(M) gene was divided to two fragments to synthesize by RT-PCR. The optimization of upstream gene sequence was carried out to improve proapo AI_(M) expression level in E. coli. After induction with a shift of temperature, yields of recombinant proapo AI_(M) achieved about 45 % of total cell protein and the recombinant proapo AI_(M) was expressed as a form of inclusion body in cells. The renaturation of protein was carried with a hydrophobic interaction column,the results showed that recombinant proapo AI_(M) had similar functional properties identical to those of native protein.