In spite of the fact that General Directorate of Pious Foundations has will to provide budget for the restoration of waqf origined monuments, there are still contradictions in the related restoration applications. There is an increase in the number of restorations and decrease in the ratio between technical staff and project number. The aim of this study is to understand effects of changes on cultural asset values of waqf origined monuments which have sustained their authentic functions, evaluate the change in the values period by period, assess the current interventions, present restoration history, and propose principles for future interventions that will sustain cultural asset value. Historical mosques in Manisa and dated to different ages are selected as case studies: Haki Baba Mosque (1371), Göktaşlı Mosque (1630-31), Kabasakal Mosque (≤1841), Pazaryeri Mosque (1874) and Çarşı Mosque (1875). Mixed methods combining qualitative and quantitative techniques were used. In conclusion, picturesqueness value, spiritual value, virginity value, rarity value and age value of the monuments and their period by period changes are stated. Scale of intervention, delicacy of the monument and appropriateness of interventions in relation with principles such as reversibility, transmission of data, physical sustainability, and qualified design and workmanship were defined as the parameters that have direct impact on the sustaining of values. In addition, history of restoration of the studied mosques and principles for future interventions regarding similar structures are put forward.