A series of Ce1MgxZr1-xO2 mixed metal oxides with different molar ratios were prepared by simple co-precipitation and were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, temperature-programmed desorption of CO2, and N2 adsorption techniques. The prepared materials were tested for catalytic activity by the synthesis of tetrahydrobenzo[b]pyran derivatives using a three component reaction(aromatic aldehydes, malononitrile, and dimedone)in an ethanol medium. The best catalytic activity was obtained with Ce1Mg0.6Zr0.4O2. The particle size or erystallite size was estimated using the Debye-Scherrer equation. The addition of magnesium oxide into the ceria-zirconia lattice resulted in the formation of nanosized particles ranging from 5.41 to 9.78 nm. This work describes the catalytic behavior of magnesium oxide in mixed metal oxide systems.