Abstract: The present invention is directed to a process for producing CMP-N-acetylneuraminic acid (CMP-NeuAc), comprising adding to the cultured E. coli cells which has been transformed with both the DNA encoding N-acetylglucosamine-6-phosphate 2-epimerase (GlcNAc-6P 2-epimerase) and the DNA encoding N-acetylneuraminic acid synthase (NeuAc synthase) and exhibit activities of N-acetylglucosamine-6-phosphate 2-epimerase and N-acetylneuraminic acid synthase, a phosphate buffer containing baker's yeast cells, CMP, N-acetylglucosamine (GlcNAc), magnesium, xylene, glucose, and CMP-N-acetylneuraminic acid synthase (CMP-NeuAc synthase) to provide a reaction mixture, and allowing the reaction to proceed and produce CMP-N-acetylneuraminic acid (CMP-NeuAc), and wherein the process does not require adding ATP.