In enzymology, a galactose-1-phosphate thymidylyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are dTTP and alpha-D-galactose 1-phosphate, whereas its two products are diphosphate and dTDP-galactose.
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing nucleotide groups (nucleotidyltransferases). The systematic name of this enzyme class is dTTP:alpha-D-galactose-1-phosphate thymidylyltransferase. Other names in common use include dTDP galactose pyrophosphorylase, galactose 1-phosphate thymidylyl transferase, thymidine diphosphogalactose pyrophosphorylase, thymidine triphosphate:alpha-D-galactose 1-phosphate, and thymidylyltransferase. This enzyme participates in nucleotide sugars metabolism.