Adsorption of sulfuric acid anions (HSO₄⁻ or SO₄²⁻) on single crystal electrodes of platinum and palladium in 0.05 M H₂SO₄ has been studied using infrared reflection absorption spectroscopy (IRAS). Both Pt(111) and Pd(111) electrodes provide a single IRAS band around 1200 cm⁻¹ in the region above 1000 cm⁻¹. Two bands appear around 1200 and 1100 cm⁻¹ with Pt(100), Pt(110) and Pt(S)-[n(111)×(111)] electrodes. The intensity of the lower frequency band is enhanced with the increase of the step atom density. The IRAS spectra of Pd(100), Pd(110) and stepped surface of Pd (Pd(311)) differ completely from those of Pt electrodes: a single band is observed around 1200 cm⁻¹. Adsorbed geometry and adsorption site of the anion are discussed. The reduction of CO₂ is deactivated remarkably by the adsorption of sulfuric acid anion on the Pt(S)-[n(111)×(111)] electrodes. Active site for the CO₂ reduction is also discussed.