The inhibition efficiency of fluorescein in controlling corrosion of carbon steel, immersed in well water, has been evaluated by mass loss method both in the absence and presence of zinc ion. The formulation consisting of 60 ppm of Fluorescein (FN) and 50 ppm of Zn2+ offers 98% inhibition efficiency to carbon steel immersed in well water. A synergistic effect exists between FN and Zn2+. The inhibition efficiency (IE) of the FN-Zn2+ system decreases with increases in immersion period. Addition of N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB) sodium dodecyl sulphate (SDS), sodium sulphite (Na<inf>2</inf>SO<inf>3</inf>) does not change the excellent inhibition efficiency of the FN-Zn2+ system. Polarization study suggests that the FN-Zn2+ functions as an anodic inhibitor system. AC impedance spectra reveal the presence of a protective film on the metal surface. FTIR spectra indicate that the protective film consists of Fe 2+-FN complex and Zn(OH)<inf>2</inf>. © 2009 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria. © 2010 Elsevier B.V., All rights reserved.