Deuterium incorporation at the C-3 position of flavanones was achieved by treatment of flavanones and 2'-hydroxychalcones with D3PO4 and AcOD. We propose that the deuteration reaction mechanism for 2'-hydroxychalcones substrates is as follows. In the first step, 2'-hydroxychalcones cyclize to the corresponding flavanones by an intramolecular Michael-type reaction. Then deuteriums are incorporated into the flavanones via enolization.