Coadsorption of water and sulfate species with uracil was found on the gold electrode using attenuated total reflection-infrared spectroscopy. The adsorbed sulfate species vary with the pH in the electrolyte solution. The peak frequencies of the S-O stretching mode from the sulfate adspecies do not depend on the electrode potential, in contrast to the results in uracil-free H2SO4 or Na2SO4 solutions. The coadsorption of the water and sulfate species is intrinsically suppressed by a hydrophobic methyl group added to the carbon atom in the pyrimidine ring. Thus, we have detected the water and sulfate species located outside the uracil monolayer.