Abstract: Since ancient times, decoration as a complementary for the appearance was a part of original Iranian art. With prevalence of Islam, this approach entered into the process of evolution, until it flourished in Saljughi era by inventions made in this regard and in Safavid era, according to aesthetic verve of Safavid kings, it reached to its highest place. In this period, due to Safavid kings’ inclination to Shiite faith, constructing religious buildings such as Mosque, religious schools and holy shrines with decorations such as “Mogharnas”. “tile-making”, Calligraphy, fillet, etc. was intensified. The main question of the study is whether decoration works in religious buildings such as mosque or schools is aimed at intensifying spiritual feelings of the audiences or a combination of art and architecture and whether such buildings-with their aesthetic, terrestrial elements - are in conflict with the principle of avoiding Luxury and extravagance and if not, so what is the application of these decorations in such buildings that are considered as the place of meditation and thought for learning religious sciences, self-purification and reaching to divine revelation. This is a research analytic article and its data collection tool is as description, existing hypotheses and library data. In this research, first we interpret each keywords and examine theoretical fundamentals of the application of the decorations, causes and the method of using them in religious buildings of Safavid era and then we start by analyzing some significant construction of that era.