A simple, green and highly efficient approach for the one-pot three-component synthesis of β-phosphonomalonates has been developed. In the presence of the quaternary ammonium salt catalysts, the β-phosphonomalonates were obtained in excellent yields within short times via tandem Knoevenagel–phospha-Michael reaction. The reaction of aldehydes/ketones, active methylene compounds, and diethyl phosphite performed at room temperature under solvent-free conditions. No column purification is required and the products can be purified by simple crystallization. The catalysts can be easily recovered and reused several times without significant activity loss.