Expression differences of flavonoid synthase I(BmFNS I)gene in the midgut,silk gland and fat body of the male and female Bombyx Mori with sex-identified fluorescent cocoon color were detected by fluorescence quantitative PCR.The result showed that the relative expression level of BmFNS I gene in midgut of Bombyx Mori was the highest,followed by that in fat body,and the expression level in silk gland was the lowest,indicating that BmFNS I gene played an important role in flavonoids anabolism in mulberry leaves,which was the food of silkworm.However,there was no significant difference in BmFNS I gene expression level between midguts of male and female Bombyx Mori species with sex-identified fluorescent cocoon color,suggesting that there was no difference in flavonoids anabolism of mulberry leaves between the male and female Bombyx Mori with sex-identified fluorescent cocoon color,at least no difference in flavonoids anabolism regulated by FSN I gene.