Abstract: Two strains were selected from the advantage serotype strains, and the basic seeds were prepared, the cultural characteristics, immunogenicity and toxicity of the 1st, the 10th and the 13th of subcultured bacteria were determined. The results showed that the cultural characteristics, immunogenicity and toxicity of the 13th basic seed passage of E.coli. GX-5 strain and GX-21 strain didn’t change, indicating that these two isolates is a good strain for vaccine production, these studies established a basis for seed lot. And then the high-density fermentation test of the duck E.coli was conducted, the best fermentation conditions of the duck E.coli in Martin Agar Medium were the fermentation temperature 37.5 ℃, pH 7.4, initial glucose concentration 10 g/L, added sugar 10 g/L, inoculum 4%, ventilation 1 L/L·min, agitation speed 200 r/min, and after 12 h culture, the concentrations of fermentation bacteria reached the highest, D_{600 nm} value was 30.32. The study lays the foundation for the large-scale production of E.coli antigens and provids basic materials for the development of new vaccines.

Key words: Escherichia coli of duck; basic seed; high-density fermentation; fermentation conditions