Decoration in Iranian-Islamic architecture talks about the emergence of beliefs and ideals that have been localized and embodied in the body of buildings. Maknoon’s thoughts in these arrays reflect the concepts and beliefs of the spirit of the times. The presence of all kinds of motifs in architecture represents eternal ideas in a conceptual field that have emerged through symbolic motifs. Among the multitude of motifs, plant motifs have played a major role in the decorations of Iranian Islamic architecture. The cypress pattern is one of the ancient symbols that has always been manifested in various forms in the buildings of Iran from the ancient times to the Islamic era. Due to the rich content of this motif in the native architecture of Mazandaran, many and original examples of it can be seen on the structure of buildings, which indicates the valuable position of this symbol among the people of the region. The current research has been carried out with the aim of discovering the hidden and semantic layers of the role of cedar in the architecture of Mazandaran during the Qajar era, and it analyzes 18 Qajar buildings of this region with a developmental excavation based on a qualitative method and a descriptive-analytical approach. The authors are trying to answer this question by using documentary and field studies, what are the hidden and semantic layers of the role of cedar in the architectural decorations of Mazandaran during the Qajar period? The findings show that the mental motifs of the cypress pattern originated from mythological narratives, ritual beliefs and religious beliefs of the people of the region, and in combination with motifs such as animal, vegetable, geometric, asemani and calligraphy, according to the use of Qajar buildings in Mazandaran, have been expressed in the form of concepts such as fertility, blessing, immortality, freedom, uprightness and rebirth, and artists have used the symbolic aspects of this motif. Furthermore, the conscious selection of other motifs in combination with it has made a wonderful combination of pictorial codes and exemplary images objectified by using various techniques.