Abstract (PDF) Supplementary Material (PDF) Graphical Abstract: This study presents an eco-friendly method for synthesizing 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) through the Biginelli reaction. A novel Heteropolyacid-Clay (HPA-Clay) catalyst, formed by immobilizing H5PV2W10O40 on Montmorillonite KSF clay, displays enhanced stability and catalytic efficiency. Operating under solvent-free, one-pot conditions, the process delivers DHPMs with high yields and shortened reaction times. Catalyzed by 2 mol% HPA-Clay, it adheres to green chemistry principles, emphasizing cost-efficiency, environmental sustainability, and recyclability. The catalyst consistently performs over multiple cycles, showcasing promise for advancing Biginelli reactions.