The present invention concerns a process for producing nucleosides by carrying out the reaction of a base donor, a saccharide residue donor and a phosphoric acid donor by the use of an enzyme preparation containing nucleoside phosphorylase, thereby forming an N-glycosidic bond between the base moiety of the base donor and the saccharide moiety of the saccharide residue donor, which comprises using, as the enzyme preparation containing nucleoside phosphorylase, a preparation derived from the cells of one or more kinds of microorganisms belonging to thermophiles of the genus Bacillus and having high nucleoside phosphorylase activity per unit cell weight.