A method for producing lacto-N-biose I and galacto-N-biose inexpensively and conveniently is provided. The method for producing lacto-N-biose I or galacto-N-biose, characterized in that the method comprises causing: (i) a combination of a carbohydrate raw material with an enzyme that catalyzes phosphorolysis of the carbohydrate raw material to give a-glucose-1-phosphate; and (ii) a combination of an enzyme that converts .alpha.-glucose-1-phosphate to UDP-glucose and an enzyme that converts UDP-galactose to galactose-1-phosphate with their cofactors, and/or a combination of an enzyme (UDP-Gly synthase) that converts .alpha.-glucose-1-phosphate and UDP-galactose to UDP-glucose and .alpha.-galactose-1-phosphate, respectively, with its cofactor(s)to act in the presence of N-acetylglucosamine or N-acetylgalactosamine, phosphoric acid, lacto-N-biose phosphorylase (EC 2.4.1.211), and UDP-glucose-4-epimerase (EC 5.1.3.2).