Dissimilar metal welding is frequently used to join carbon steels to other materials such as nickel metal. This approach is most often used where a transition in mechanical properties and/or performance in service are required. The power generation industry uses dissimilar metal welding extensively to reduce material costs and enhance performance in elevatedtemperature applications.Anodic polarization curves for deposited as weldcondition of Ni weld metal on carbon steel in 3.5% NaCl solution having neutral pH are studying. Anodic polarization curve for thermal aging of Ni weld metal for different agingtimes50,500 and 1000 hr at 550ºCare also recorded. The results indicated that the corrosion current of the Ni weld metal on carbon steel increases as aging time increase,also the grain size of the deposited Nickel increase during thermal aging for different times 50, 500 and 1000 hours respectively