The electron capture dynamics of hydroperoxy radical-water complexes have been investigated by means of direct density functional theory (DFT) molecular dynamics (MD) method to elucidate the solvation (hydration) effect on the reaction mechanism. The complexes composed of HOO and one to four water molecules, HOO(H(2)O)(n) (n = 1-4), were considered to be the hydrated HOO system. After the electron capture of n = 1, only solvent reorientation of H(2)O around HOO(-) occurred, and a stable complex (HOO(-)-H(2)O) was formed within 100-300 fs. In the case of n = 2-4, a proton of H(2)O was transferred from H(2)O to OOH(-), whereas H(2)O(2) and OH(-)(H(2)O)(n-1) were found as products. It was suggested that the HOO radical adsorbed on water cluster is efficiently converted in the H(2)O(2) without activation barrier after the electron capture of HOO. Time scales of proton transfer were calculated to be 200-300 fs. The mechanism of electron capture of HOO in polar stratospheric cloud was discussed on the basis of theoretical results.