Dinuclear titanium, zirconium, and hafnium oxide clusters, M2O2 and M2O4 (M = Ti, Zr, Hf) have been prepared and characterized by matrix isolation infrared spectroscopy and quantum chemical calculations. The M2O2 clusters were formed through the reactions of metal dimers and O-2 in solid argon upon sample annealing. Theoretical calculations indicate that the Ti2O2 cluster has a singlet ground state with a nonplanar cyclic C-2v structure with a strong Ti-Ti bond, while the Zr2O2 and Hf2O2 clusters have planar cyclic structures. The M2O4 clusters were characterized to have a closed-shell singlet ground state with a nonplanar C-2h symmetry, which were formed from the dimerization of the metal dioxide molecules.