In enzymology, a 1-deoxy-d-xylulose-5-phosphate synthase (EC 2.2.1.7) is an enzyme in the non-mevalonate pathway that catalyzes the chemical reaction

pyruvate + d-glyceraldehyde 3-phosphate ${\displaystyle \rightleftharpoons }$ 1-deoxy-d-xylulose 5-phosphate + CO₂

Thus, the two substrates of this enzyme are pyruvate and d-glyceraldehyde 3-phosphate, whereas its two products are 1-deoxy-d-xylulose 5-phosphate and CO₂.

This enzyme belongs to the family of transferases, specifically those transferring aldehyde or ketonic groups (transaldolases and transketolases, respectively). The systematic name of this enzyme class is pyruvate:d-glyceraldehyde-3-phosphate acetaldehydetransferase (decarboxylating). Other names in common use include 1-deoxy-d-xylulose-5-phosphate pyruvate-lyase (carboxylating), and DXP-synthase. This enzyme participates in biosynthesis of steroids.

As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2O1S and 2O1X.