Magnesium oxide-supported polytitazane cobalt complex has been prepared and found to be a very effective catalyst for the epoxidation of alpha-pinene in the presence of an aldehyde as a reductant. XPS data show that the high valent cobalt(III) was stabilized by the mutidentate nitrogen ligand of polytitazane. The alpha-pinene oxide can be obtained in 96.0% yield with 96.6% selectivity at 25 degrees C under an atmospheric pressure of molecular oxygen. Isobutyraldehyde is an effective reductant and only 1.2 equivalent of isobutyraldehyde to alpha-pinene is needed to ensure high yield of alpha-pinene oxide. The catalyst is also very stable and can be reused at least eight times without loss of its activity.