In enzymology, an oxaloacetase () is an enzyme that catalyzes the chemical reaction:
Thus, the two substrates of this enzyme are oxaloacetate and H<sub>2</sub>O, whereas its two products are oxalate and acetate.
This enzyme belongs to the family of hydrolases, specifically those acting on carbon-carbon bonds in ketonic substances. The systematic name of this enzyme class is oxaloacetate acetylhydrolase. This enzyme is also called oxalacetic hydrolase.