Abstract: The function of gene bagJ via in-frame deletion in Streptomyces sp.Tü 4128 was identified.The result of HPLC analysis showed that the production of bagremycins was significantly decreased in the single knock-out strain of bagJ.The production of bagremycins was recovered in the complementation strain.The overexpression of gene bagJ resulted in producing far more bagremycins,which indicated that bagJ was indispensable in the biosynthesis of bagremycins.The test of inhibition zones showed that the bagJ mutant was more sentitive to bagremycins than the wild type.Heterogenous expression of BagJ in Streptomyces lividans TK64 enhanced its endurance to bagremycins which suggested that bagJ might be a resistant gene of the novel antibiotics bagremycins.SEM showed that the morphology of the mycelia was changed in the heterogenous expression strain of BagJ in S. lividams TK64.The sensitivity assays of other antibiotics showed that BagJ was probably an antiporter.