The most important reason for the enrichment of decorative arts (especially illumination art) in Islamic societies in various periods is the prohibition of depiction in Islam. The art of illumination, which was mostly used to decorate the Qur'an in different historical periods of Iran, including the Great Seljuk period, was influenced by the arts of previous periods and became a source of creativity and inspiration for Muslims and sometimes non-Muslim artists in other countries. This research was carried out in order to examine the status and general characteristics of illumination art during the Great Seljuk period. The descriptive-analytical method was used in the research. As a result, during the Great Seljuk period, the Qur'an manuscripts were made of paper instead of leather. The richness of motifs, patterns and colours, the use of various colours and geometric arrangements draw attention to the illuminations of this period. According to the results of this study, the most important illumination examples of the Great Seljuk period were used in the Quran manuscripts. In these manuscripts, it is seen that motifs such as schemes, six and eight-pointed stars and golden circles are used to decorate the headlines (serlevha pages), the heads of the sura, the interlines and zahriye parts. In addition, the illumination samples of the Great Seljuk period positively affected the later periods, especially the Ilkhanid and Memlukid periods, as well as all other arts. Great Seljuk elegant illumination samples with the beauty of their patterns, the order and delicacy of the motifs and the use of colours are masterpieces of Islamic art.