Abstract: The Actinobacillus pleuropneumoniae serotype 10 strain which was isolated from Shandong province had been cultivated in the LB medium containing 0.02%NAD、5% Newborn Calf Serum、1mM CaCl2 .The ApxⅠtoxin was purified by precipitation with ammonium sulfate and chromatography on Sephadex G-200. In the Pathogenicity experiment, Karber’s method was used to test the LD50 of the ApxⅠtoxin in mice by intraperitioneally injection. To study the ApxⅠtoxin’s immunoprotection, the purified ApxⅠtoxin was emulsified with Freund’s adjuvant and vaccinated the mice twice with a 2-week of interval. Two weeks after the second vaccination, the mice were challenged intraperitioneally with APP serotype 10.The mice were immunized at 30 days and 45 days with the optimization immunizing dose, then the mice were challenged with the APP of serotype 1,3,5 and 7 at 60 days. The result of the LD50 of the ApxⅠtoxin injection in mice was 80.9mg/Kg, with a 95% confidence limit of 63.2 mg/kg ~103.5 mg/kg; the ApxⅠtoxin had a good immunogenicity and 40μg per mouse was the optimization immunizing dose.