The Al-Ghuri mausoleum in Al-Muizz ll-Din Allah street dating from 909-910 A.H/ 1504-1505 A.D., list No 65. This type of historical buildings have been inhabited for a long period were left exposed to climatic deterioration until 1999, when a general program of the historic Cairo project undertook a study of the degradation processes affecting the interior facings of mausoleum. This started with field-based observation of the monument's condition and, description of the building materials, (limestone, marbles and mortar). Moisture and salt decay processes are amongst the most recurrent causes of damage of built objects and monuments. Although salt damage has been intensively investigated for several decades, the mechanisms and factors that control salt transport, accumulation, and crystallization in porous media and the development of damage are poorly understood. Knowledge about the transport of water and ions and salt crystallization in masonry (in the paper referred to as substrate) and plasters is needed to explain salt damage and to develop durable materials.  In 2000, samples of the building material were collected on site and laboratory studies of those samples were carried out in the Department of Mining at the Cairo University. The cryslization and efflorescence of salts on limestones and marbles interior facings of the Al-Ghuri mausoleum were comprehensively examined. Several salts were identified (halite, thenardite, gypsum, soda-nitre), mainly dispersed in the marble slabs of the first two registers. For a better understanding of the origin and formation mechanisms of these salts, thin section examination, x-ray diffraction investigations were carried out on the neoformation of salts themselves and on cores of the materials composing the walls. The results of this research indicated that the main causes of the formation of salt efflorescence and crystals are connected to condensation and evaporation, an increasing of the moisture content of the walls, and to the connected mobillity of soluble cations.