This invention provides to a novel gene encoding a protein aving the activity of &bgr;-galactoside-&agr;2,6-sialyltransferase. The gene of the invention encodes a protein which having the amino acid sequence of SEQ ID NO:1, or a protein having the amino acid sequence of SEQ ID NO:1 which have been modified by deletion, substitution or addition of at least one amino acid residue in said sequence, while maintaining substantially the same &bgr;-galactoside-&agr;2,6-sialyltransferase activity. The present invention uses said gene to further provide a vector for expressing a protein having the &bgr;-galactoside-&agr;2,6-sialyltransferase activity, host cells and a recombinant protein. The protein encoded by the gene of the invention does not have any substantial homology with known sialyltransferases, and in addition, the membrane binding region is located in the C-terminal unlike known sialyltransferases.