In enzymology, a RNA uridylyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are UTP and RNA<sub>n</sub>, whereas its two products are diphosphate and RNA<sub>n+1</sub>.
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing nucleotide groups (nucleotidyltransferases). The systematic name of this enzyme class is UTP:RNA uridylyltransferase. Other names in common use include terminal uridylyltransferase, and TUT.
As of late 2007, 8 structures have been solved for this class of enzymes, with PDB accession codes , , , , , , , and .