Diethyl maleate is an organic compound with the CAS Registry number 141-05-9.

[2][3][4] One of the key uses for the compound is in production of the pesticide Malathion.

[6] It has been studied extensively with regard to renal function.

[7] Other medical uses include treatment of breast cancer and its monitoring with Positron Emission Tomography.

In synthetic organic chemistry it is a dienophile and used in the Diels-Alder reaction.