Gap junctions that allow for a direct exchange of second messenger and ions are the most conserved cellular structures in multicellular organisms. We have isolated and characterized a Bombyx mori gene innexin3 that encodes a new member of the innexin family required for the early embryonic development. The BmINX3 mRNA was 1,814 nucleotide residues in length, and the deduced amino acid sequence of BmInx3 shared 74% similarity with Apis melifera innexin3. The expression profile of the BmINX3 mRNA is similar to that of previously described BmINX2, expressed in ovary and testis after 5th instar larvae and in fat body after gut purge. However, during embryogenesis, the expression of BmINX3 mRNA is restricted to the blastokinesis stage. Microscopic observation of the BmInx2 and BmInx3 fused to fluorescent proteins showed an overlapping cytoplasmic expression, whereas the BmInx4 is accumulated in the cytoplasmic surface at which two cells have physical contact. This finding of innexins distribution in silkworm would provide an essential basis for future studies of the functions and interactions of innexins.