In enzymology, a mannose-1-phosphate guanylyltransferase (GDP) () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are GDP and alpha-D-mannose 1-phosphate, whereas its two products are phosphate and GDP-mannose.
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing nucleotide groups (nucleotidyltransferases). The systematic name of this enzyme class is GDP:alpha-D-mannose-1-phosphate guanylyltransferase. This enzyme participates in fructose and mannose metabolism.