The alkaline substance from concrete has already been identified as ammonia, and the condition of formation of ammonia, and the condition of formation has been studied. This paper reports on the investigation made of the mechanism of ammonia formation from concrete which adversely affects objects of art. On examining the mechanism of formation, it has been found that the amount of ammonia is determined by the aggregates in the concrete and the cause of formation is the nitrogeneous impurities contained in the aggregates. Causes of ammonia formation differ in natural river aggregates ad slag aggregates nitrogenous organics on the surfaces, which in the latter it is the nitrogenous substances contained in the aggregates due to nitrogen absorbed from the air during the manufacturing process.