A practical large-scale synthesis of monomethyl malonate and monoethyl malonate, which are among the most commonly applied half-esters in organic synthesis, is described, applying the highly efficient selective monohydrolysis of symmetric diesters we reported before. The optimal conditions with regard to the type of base, equivalent, co-solvents, and the reaction time have been examined for large-scale reactions. Monomethyl malonate and monoethyl malonate were obtained in high yields with near 100% purity within only half a day. The conditions of this selective monohydrolysis reaction are environmentally benign and straightforward, as it requires only water, a small proportion of a volatile co-solvent, and inexpensive reagents, and produces no hazardous by-products, and therefore the synthetic utility of this reaction in process chemistry is expected.