The preparation and physical characterization are reported for a novel single-molecule magnet [Mn12O12(OAc)(12)(dPP)(4)] (dppH = diphenyl phosphate) with no coordinating water molecules. The crystal structure analysis reveals that there are four five-coordinate Mn-III ions with Mn...H approaches. Addition of water in CD2Cl2 solution was monitored by H-1 NMR, which showed that H2O could coordinate to a vacant site of a five-coordinate Mn-III ion in solution. The measurements and analyses of magnetization hysteresis and ac magnetic susceptibility indicate that the title complex is a single-molecule magnet with a quantum tunneling behavior, whose ground state was tentatively assigned to S = 10 with g = 1.78 and D -0.60 K.