In order to investigate the possibility of using red mud by-product from the aluminum industry) as a pozzolan in the cement and concrete industries, tests were carried out to examine the pozzolanic properties of calcined red mud. It was found that the red mud had the maximum reactivity when calcined at 600 deg C, because on hydration the lime content of the blended cement was considerably reduced. Very good compressive strengths were obtained with the blended cement containing 30 % calcined red mud. Mortars cast with these blended cements were placed in solutions of sea water and acetic acid. The results indicated good stability of mortars to these environments.