Abstract: The crude capsular antigen (CCA) has been extracted by using 2.9% NaC1 solution and SDS from pasteuralla multocide strain C4S-1. Under an electronic microscope, the capeula of pasteuralla multocide was found a C spiral structure of blossom or irregular form. By chemical assay, it shows a polysaccharides-protein complexes. Mice, 20-day-old and adult ducks inoculated by the antigen are no side-effecte, and shows a good immunogenicity. With antigen containing protein 1.41-2.15mg to vaccinat 8 groups of duck through intramuscular and subcuticilar way after 15 days, the protective rate is up to 80%. Nine replicated tests have been conducted, and the protective rate is 85-100%. It shows that the efficiency is stable and reliable. CCA immune duration could sustain 5-5.5 months and the protective rate is over 75%. This has been done in the fields in several provinces of China, and the Protective rate shows similarly to that have been done in the laboratory.CCA has been vaccinated to laying ducks, and it shows no significant difference in the rate of egg-production between control group and test group both in the fields and laboratory, and it also could be used to control the disease when it is breaking out. A Subunit vaccine Can be made by CCA to prevent fowl cholera, and the vaccine could be adopted by factory and Produce in large quantities.