The interaction potentials between O(1D) and methane and the potential surface for the reaction have been calculated by the ab initio MRDCI method. The minimum energy path of the reaction is an almost collinear approach of O(1D) to one of the hydrogen atoms of methane up to the position of r(OH) = 1.66 angstrom. A very low potential barrier (2.1 kcal mol-1) exists along the path, and then the oxygen atom migrates off-axis. The surface correlates to the stable methanol structure. The product channel to yield CH3 + OH and also the one to yield CH3O + H are both directly derived from the potential minimum corresponding to the stable methanol structure without any exit potential barriers. Possible reaction dynamics on the surface are discussed.