According to the analysis of large scale EST sequencing of silkworm, Bombyx mori, we found that chi, glue and fruA of silkworm have very high homology at amino acid level and closely phylogenetic relative with that of microorganism, but lower similarity with genes of eelworm (Caenorhabditis elegans), fruitfly (Drosophila melanogaster), mosquito (Anopheles gambiae) and other relative insects, respectively. It indicates that each of them is likely to have common ancestor with that of microorganism. Namely, microbial genes were likely transferred to silkworm by horizontal gene transfer, instead of the vertical inheritance in evolutionary manner.