In dual purpose water/power co-generation plants, the presence of high concentration of Cu and Ni in the re-circulating brine/condensate as a result of condenser tubes corrosion has been attributed as one of the several causes of corrosion damage of flash chamber materials and water touched parts of the boilers. The present investigation deals with the effect of dissolved nickel in the concentration range of 10 ppb to 100 ppm on the corrosion behavior of mild steel and SS 304L in two aqueous medium namely, distilled water and artificial seawater. The effect of pH, dissolved oxygen and flow condition of aqueous medium on the corrosion behavior was also monitored. The experimental techniques include immersion test and electrochemical tests which include free corrosion potential measurements and potentiodynamic polarization measurements. The corrosion rate of mild steel and SS 304L under different experimental conditions was determined by weight loss method and spectrophotometric determination of iron ion entered into the test solution during the period of immersion. The pH of the test solution was also monitored during the entire period of immersion. The left over nickel ions present in the test solution after completion of immersion was also estimated using Atomic Absorption Spectrophotometer. The surface morphology of the corroded steel surface was also examined using scanning electron microscopy (SEM). The results of the studies show that SS 304L largely remains unaffected in both distilled water and artificial seawater under different experimental conditions. However, the effect of nickel on the corrosion behavior of mild steel is quite pronounced and follows interesting trends.