【Abstract】 Objective To study plasma protein changes in chronic severe hepatitis B after plasma exchange (PE), to provide new clues for the understanding of PE mechanism, and to seek the new therapeutic targets for patients with chronic severe hepatitis B. Methods Plasma samples were obtained from chronic severe hepatitis B patients before and after PE. After removal of high abundance proteins in plasma, proteins in samples were separated by two-dimensional electrophoresis. The gels were then stained by silver nitrate or Coomassie blue, and analyzed by the Imagemaster software. Proteins in the spots showing remarkable intensity difference before and after PE were identified by electrospray ionization mass spectrometry (ESI-MS/MS). Results After the pretreatment procedures, the high abundance proteins such as albumin and IgG in the samples were mostly removed, and the low abundance proteins were enriched. From the silver stained gels, 297 protein spots from samples before PE and 305 protein spots from samples after PE were separated. From these spot, 15 proteins were found to have 3-fold differences before and after PE, and 5 proteins were identified. After PE, complement factor B precursor, CD5 antigen-like precursor, fibrinogen beta chain precursor and haptoglobin precursor were up-regulated, and apolipoprotein E precursor was down-regulated. Conclusion We have identified 5 plasma proteins showing remarkable difference in expression level before and after PE. These proteins are involved in lipoprotein metabolism, protein synthesis and catabolism, and activation of complement bypass route. They are worthwhile to be further investigated for understanding the mechanism of PE