The corrosion inhibition efficiency of methyl orange in controlling corrosion of carbon steel immersed in well water has been evaluated by weight loss method both in absence and presence of zinc ion. A synergistic effect exists between methyl orange (MO) and Zn2+. The inhibition efficiency (IE) of the MO-Zn2+ system decreases with increase in immersion period. Polarization study suggests that the MO-Zn2+ system functions as a mixed inhibitor system. FTIR spectra indicate that the protective film consists of Fe2+-MO complex and Zn(OH)(2).