The synergistic effect of carboxylates and Zn2+ on the inhibition of corrosion of mild steel in aqueous medium containing 120 ppm of Cl- has been evaluated in the present study. The inhibitors used in the present study are succinic acid (SA), malic acid (MA), sodium potassium tartrate (SPT) and aspartic acid (AA) with zinc sulphate. The biocides selected for the present work are N-cetyl - N, N, N - trimethyl ammonium bromide (CTAB) and N-cetyl pyridinium chloride (CPC). The methods used for the present study includes weight loss method, polarization studies, AC impedance and FTIR spectroscopy. On the basis of results obtained from weight loss method, other studies are carried out. Biocidal studies are carried out by using the biocides CTAB and CPC. The system consisting of 120 ppm of Cl-, 250 ppm of SPT, 25 ppm of Zn2+ and 150 ppm of CTAB shows 98% IE and 100% biocidal efficiency. The findings of this study will be useful in cooling water technology.