In enzymology, a cellobiose phosphorylase (EC 2.4.1.20) is an enzyme that catalyzes the chemical reaction

cellobiose + phosphate ${\displaystyle \rightleftharpoons }$ alpha-D-glucose 1-phosphate + D-glucose

Thus, the two substrates of this enzyme are cellobiose and phosphate, whereas its two products are alpha-D-glucose 1-phosphate and D-glucose.

This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is cellobiose:phosphate alpha-D-glucosyltransferase. This enzyme participates in starch and sucrose metabolism.

As of late 2006, two structures have been solved for this class of enzymes, with PDB accession codes 2CQS and 2CQT.