Time-averaged and time-resolved optical emission spectroscopy (OES) has been performed on three-dimensionally integrated micro-solution plasma (3D IMSP). In comparison with that of a conventional solution plasma generated in pure water vapor bubbles, the OES spectrum of our 3D IMSP, which is generated in Ar gas bubbles surrounded with water, shows more pronounced optical emission of OH radicals than of H and O radicals. In addition, time-resolved OES shows that the optical emission of OH radicals is sustained even after the emission of H and Ar almost disappears. The mechanisms of these phenomena are discussed by considering the dissociative recombination of H2O+ and/or H3O+ with low-temperature electrons.