Abstract: A purification method combined with cellulase digestion and differential centri-fugation was found ot purify the pathogen from priwinkle plants infected with citrus yellow shoot,The solution consisting of O.1mol/LMgCl2,O.5 mol/L D-mannitol,O.6mol/L glycine was used as the medium for the isolation and purification.The results obtained in the present study showed that the yield of the pathogen purified was higher,and the external morphology,the transparency af wall-membrane structure and internal structure of the pathogen were better maintained.Meanwhile,the purification method gave consistent results in different replications.The purified pathogen of citrus yellow shoot obtained with the method mentioned abore was used as antigen to immunize mice for the preparation of ascitic fluid.It was shown that the antibodies in the fluid had specific response,The micro-precipitation titer was 1:640,the titer of ring surface agglutination reaction 1:8,and that of immunosorbent electron microscopy 1:320.NO reaction was observed in the agar gel double diffusion assay test.Controls all showed negative reaction.The isolated and purified pathogen was thus recognized to have biological activity of specific antigen.