Several international conventions and charters which issued by ICOMOS reviewed the idea of completion historic buildings. Some supported the absolute thought of completion and the need to adapt it as one of the necessities of conservation operations, so as to put the fingerprint of current modern technologies on restoration and preservation processes while others went to keep this process at the minimum intervention level. With using the original materials at the restoration process, this paper highlighted charters and conventions contribution to the idea of completion. research problem pointed to the close connection between the completion and the authenticity regarding the decisions of restoration of the historic buildings, This was discussed by examining the status of the restoration of Prince Taz Palace project, which occurred in a partial collapse made an alarm to start the restoration work and resulted set of decisions related to the idea of completion, which has developed its philosophy according to the changing cases that appeared in the palace, and also the completion works varied not only at the level of intervention, but also at its kinds as structural, architectural and fine art elements, The study focused on the descriptive methodology and analytical approach through the selected case study. The research concluded that the philosophy of completion varies according to each case. And one building can include several levels of completion provided that there are archaeological and documentary evidence to prove this.