Plant expression vectors comprising an ORF of an isoform gene (&bgr1,4GT5) of human &bgr1,4-galactosyltransferase were constructed. Then, the vectors were introduced into tobacco using plant gene-recombination techniques, and transformed tobacco was made. Analysis of the obtained transformed tobacco showed that more than 200 &mug of lactosylceramide was produced from 1 g of fresh leaves. Accordingly, the present invention made it possible to mass synthesize lactosylceramide by using recombinant plants.