Abstract: The optimum medium and culture conditions of the Xenorhabdus sp. D43 s
train were studied. The relationships between antibiotic activity and pH, reducing sugar, total sugar, aminonitrogen in process of fermentation were analyzed. The optimal medium was maltose 05%, peptone 10%, beef extract 0.5%, CaCl₂ 0.5% and KNO₃ 0.02%. Stock cultured for 16 h and primary pH of medium ranged from 6.0 to 8.0, fermentation for 72 h were of benefit to the yield of antibiotic. The pH, reducing sugar and total sugar in process of fermentation were related to the antibiotic yields. The yield of antibiotic increased to 46.67% compared with the basic medium.