A catalytic system for activation of CH4 under mild conditions is in high demand. In this study, Ga-oxo clusters in CHA zeolites were prepared by reductive solid-state ion-exchange followed by O-2 treatment. Formation of the Ga-oxo clusters was demonstrated using X-ray absorption fine structure (XAFS) measurements. Plausible models of the cluster were developed by using an ab initio thermodynamic analysis. Importantly, the CHA zeolite-supported Ga-oxo clusters promote partial oxidation of CH4 to yield adsorbed formaldehyde and formic acid. The results of density functional theory (DFT) calculations, designed to gain information about the mechanism of the process, show that the Z(2)[Ga-2(O)(OH)(2)] is likely the most active cluster for C-H bond activation of CH4. Observations made in this experimental and theoretical effort demonstrate that main-group metal-oxo clusters have the potential of serving as active species for transformations of CH4.