In enzymology, a nucleoside ribosyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are D-ribosyl-base<sub>1</sub> and base<sub>2</sub>, whereas its two products are D-ribosyl-base<sub>2</sub> and base<sub>1</sub>.
This enzyme belongs to the family of glycosyltransferases, specifically the pentosyltransferases. The systematic name of this enzyme class is nucleoside:purine(pyrimidine) D-ribosyltransferase. This enzyme is also called nucleoside N-ribosyltransferase.