Aeromonas hydrophila is one of the important pathogenic bacteria of aquaculture. It is significant , therefore , to study the changes on functional genome in its growth cycle. Two2dimensional electrophoresis (22D PAGE) , one of the approaches for proteomics , was used to study protein composition in different phases during the cycle. The result showed that the composition was significantly changed in different phases. The discovery of different pertinent proteins in the different growth phases will contribute to find out the genome expression of A. hydrophila in different growth phases. In this experiment 22D PAGE was compared with normal SDS2PAGE in the same conditions , and the result indicated that 22D PAGE was an effective technique for proteomics study.