This paper is the 3rd one in a series of papers concerning the environmental factors affecting the archaeological buildings in Egypt. It presents the results of scientific studies and examinations carried out to evaluate the deterioration conditions which affected archaeological buildings in coastal environment. In Alexandria there are many monumental sites and stone buildings that have suffered from many aggressive factors of deterioration (chemical, physical and biological) which have caused great harmful appearances and threatening to destroy it completely. These effects include the chemical actions resulting from seawater and sea spray, and mechanical actions of water waves. (Qait bey castle) as a case study was periodically investigated by many scientific techniques through 5 years in order to check their decay conditions and to define the most suitable conservation approaches and non-destructive methods for preservation. Different techniques and examination were performed to evaluate its current deterioration state of stone materials such as XRD which was used for studying the mineralogical compositions. AAS was used for studying chemical constitutes of sea water, as well as, SEM that was used to investigate the samples morphological characteristics in addition to studying some species of microorganisms, our results proved that the castle was highly affected by severe deterioration effects through the collaboration between chemical, mechanical and biological mechanisms. These mechanisms lead to several appearances such as honeycomb, colored hard crusts, mortars desegregation, stone appearance changes, growing and accumulating some microorganism's species, pitting, and scratch and granular disintegration.