Abstract: Two-component system is an important regulatory mechanism of secondary metabolite biosynthesis in Streptomyces. Based on bioinformatics analysis, we found that two-component system SAV931/932, located on the upstream of avermectin biosynthesis cluster, may have some effects on regulation of avermectin biosynthesis. Deletion of SAV931/932 resulted in the increase of avermectin production by more than 25%, and faster mycelium growth in the prophase of fermentation. RT-PCR showed that the transcription level of the structure genes, aveA1, aveA3 and the regulatory gene aveR involved in avermectin biosynthetic pathway were all up-regulated. These results demonstrated two-component system SAV931/932, to some extent, inhibited avermectin biosynthesis. These results may be helpful to better understand the regulatory mechanism of the second metabolite and improve avermectin production in streptomyces avermitilis.