A novel, green, and sustainable method for the synthesis of octahydroquinazolinones has been developed using a solvent-free and catalyst-free grindstone (mechanochemical) approach. This one-pot, three-component reaction involves the condensation of aromatic aldehydes, dimedone, and urea under ambient conditions without the need for solvents or catalysts. The method affords high to excellent yields (85–95%) with short reaction times (10–15 min) and minimal purification. The synthesized compounds were characterized by FT-IR, ¹H NMR, ¹³C NMR, and mass spectrometry. The environmental impact was minimized by eliminating hazardous reagents, heating, and work-up procedures. This methodology offers a practical and scalable solution aligned with green chemistry principles.