Historical structures in Palestine are subjected to various types of damages due to natural or manmade causes that result in sudden destruction or progressive deterioration. “Siad Hashim” mosque has been subjected to progressive deterioration due to long neglect, abuse, environmental factors, inadequate design and construction, soil settlement, damping, growth of vegetation and other factors that led this structure to a critical condition. This paper describes the nature, cause, assessment and rehabilitation measures corresponding to existing damages. Recent rehabilitation carried out in the structure is also described, emphasizing the criteria and techniques adopted and the underlying studies and analyses. The repair and strengthening carried out to the mosque have not only succeeded in restoring its original conditions but also upgraded its ability to carry applied loads and actions satisfying current code requirements.