Abstract: A virulent strain of Escherichia coli had been isolated and found to be the pathogen of piglet dysentery by Mr.Li Xue-liang (Yunnan Institute of Animal Husbandary and Veterinary Medicine).When 6×107 living bacteria of the virulent strain were injected subcutaneously into each mouse,all the injected mice would be killed.Ribosomal preparations were isolated from disrupted cells by a modification of the ammonium sulfate precipitation method described by C.G.Kurland (1966),omitting the ultracentrifugation step.The ribosomal preparation was proved to be highly immunogenic for mice and immunization with the preparation elicited significant protective immunity.The effect was obvious when mice immunized subcutaneously with ribosomal preparation without adjuvant were challenged subcutaneously with 2-2.4×108 living bacteria two weeks after immunization.