The effect of thiourea on copper was investigated in solutions of sulfuric acid. Weak interaction occurs at low concentrations of thiourea. At high concentrations of thiourea (>1 mM), strong effects were observed. Thiourea forms complexes with cuprous ions in solution which shift the open circuit potential of the copper electrode in a negative direction and causes copper to dissolve to cuprous species even in sulfate media. At more positive potentials, thiourea reacts with cupric ions and forms a complex. At a sufficient concentration of the cupric-thiourea complex, a sulfate complex film forms. The film can be formed reversibly upon cycling the copper electrode potential.