Abstract:The isolate GN52 of Riemerrella anatipestifer was passaged on the Martin Medium successively according to the optimum condition. The experiments included Gram staining, biochemical test, drug sensitivity test and animal experiments were carried out on the bacteria of 3rd, 11th, 21st, 31st, 41st, 51st and 61st generations. It indicated that the bacterial morphs, biochemical character, drug resistance of the strain had no obvious change, but the virulence showed a trend of reduction.