Corrosion of reinforcement embedded in concrete is the most common cause of failure in concrete structures. The work is being carried out to investigate the rate and amount of corrosion of steel in concrete where cement is replaced by slag in different proportions. This paper reports a detailed corrosion study, carried out on concrete containing blast furnace slag. The study encompasses slag collected from several premier steel plants in India. Corrosion of steel was examined electrochemically through potentiodynamic study and also by accelerated corrosion study. Micrographic study was also carried out to examine the alteration of pore structure of slag concrete. These studies reveal that increase in slag proportion decreases the rate and amount of corrosion of reinforcement embedded in slag concrete.