The Manichaean manuscripts and the Abbasid Qur'an are among the most prominent examples of book art in the Manichaean and Islamic religious traditions. Manichaean manuscripts, rooted in the mystical beliefs of Manichaeism, exhibit a distinctive structure in writing and decoration. These texts showcase visual and spiritual creativity through the use of alternating red and black scripts to distinguish paragraphs, unique punctuation marks (such as dots at the beginning and end of sentences), intricate floral motifs, elaborate marginal decorations, and the application of gold to symbolize the concepts of light and darkness. In contrast, the Chester Beatty Qur'an, a distinguished example from the Abbasid period, embodies the characteristics of Islamic art with its angular Kufic calligraphy, geometric and floral illuminations, and emphasis on the majesty of the divine word. The research questions are as follows: What was the writing structure of Manichaean manuscripts, and which elements were used for decoration and to what purpose? The findings reveal that Manichaean manuscripts adhere to specific writing conventions, including the use of alternating scripts, consistent punctuation, and rich decorations such as floral motifs, multilayered marginal designs, and gold to emphasize mystical concepts. A comparative analysis with the Abbasid Qur'an demonstrates shared elements, including the use of gold, floral motifs, intricate marginal decorations, elongated script, and certain punctuation marks. These commonalities, particularly in floral illuminations and the symbolic use of gold, indicate the influence of the Manichaean tradition on the development of Islamic book.