In enzymology, an amylosucrase (EC 2.4.1.4) is an enzyme that catalyzes the chemical reaction

sucrose + (1,4-alpha-D-glucosyl)n ${\displaystyle \rightleftharpoons }$ D-fructose + (1,4-alpha-D-glucosyl)n⁺1

Thus, the two substrates of this enzyme are sucrose and (1,4-alpha-D-glucosyl)n, whereas its two products are D-fructose and (1,4-alpha-D-glucosyl)n+1.

This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is sucrose:1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase. Other names in common use include sucrose-glucan glucosyltransferase, and sucrose-1,4-alpha-glucan glucosyltransferase. This enzyme participates in starch and sucrose metabolism.

As of late 2007, 10 structures have been solved for this class of enzymes, with PDB accession codes 1G5A, 1JG9, 1JGI, 1MVY, 1MW0, 1MW1, 1MW2, 1MW3, 1S46, and 1ZS2.