Abstract:Glucan is the production of sucrose ferment， small molecular weight glucan （which is also called dextran） obtained after hydrolisis and purification with certain molecular weight， and high homogeneous is the internationally recognized high quality blood plasma substitution. However， the present production technique of dextran can inaccessibility meet the clinical medicine standard， therefore， it has the very obvious practical sig－ nificance and the theory value to develop a new way that can synthesize dextran with specific molecular weight distribution. By HPGPC on-line detection of molecular heavy weight of fermentation products， we can control the molecular weight of Leuconostoc Mesenteroides fermentation products by immobilization technology，we found that the amount of immobilized bacteria fermentation of glucan were more than the free bacteria fermenta－ tion in the same time； and the molecular weight of dextran from immobilized bacteria fermentation produce was lower than dextran from free bacteria fermentation in the same time.