Phtalimidine finds wide pharmaceutical applications and its deuterated derivative is supposed to exhibit enhanced stability towards metabolism. In this work, an electrochemically reductive deuteration strategy from phthalinmide to phtalimidine-d2 was achieved with D2O as a deuterium source at the reagent level in common solvents. This approach showed broad compatibility with a variety of functional groups. Mechanistic investigations assisted by electrochemical analysis revealed a 4-electron reduction pathway, and the coupled anodic oxygen evolution collectively maintains a neutral to mild basic conditions for the ongoing electrochemical reaction.