We have proposed a novel method for synthesizing K-substituted LaMnO3 ternary nanostructures under hydrothermal conditions and evaluated their morphological and catalytic properties. The catalyst prepared in this method exhibits improved catalytic activity for the selective reduction of α,β-unsaturated carbonyl compounds and nitroarenes compared with most literature reports. These nanostructures are inexpensive, abundant, nonpyrophoric, and stable, thus making them better choices than conventional precious metals. These principles, coupled with improved nanoscale synthesis, could expand the application of heterogeneous catalysis.