As far as we know, no book was ever written in Persian during the early centuries of the history of Islam on philosophy or any other field, and all Muslim scientists and scholars, who were mostly Iranian, wrote their scientific works in Arabic. From fourth century (AH) onwards, Iranian philosophers gradually started writing a limited number of their works in Persian alongside the many works in Arabic. This was an invaluable endeavor since it paved the way for later scholars to write in Persian. They did so at a time when Persian, after an interval, lacked the necessary capacity for the expression of abstract philosophical concepts and meanings. Ibn Sīnā and his students, Nāṣir Khusraw, Suhrawardī, Bābā Afḍal Kāshānī, Khwājah Naṣīr al-Dīn Ṭūsī, Quṭb al-Dīn Shīrāzī, and many others played a significant role in writing philosophical works in Persian. Their attempts at finding Persian equivalents for Arabic philosophical terms have been of great value to Iranian philosophers of the modern period to create Persian philosophical works. Following a descriptive-analytic method, this paper investigates the linguistic and literary reasons behind the dominance of Arabic over philosophical writings. Moreover, through introducing the most important philosophical writings in Persian, it explains their role in the development and enrichment of this language for the transfer of philosophical knowledge. Finally, the author discusses the effects of translated western philosophical works on the enrichment of the treasure of Persian lexicon and emphasizes the necessity of writing more philosophical works in Persian in the present era, in which the number of people who speak Arabic as a foreign or second language has decreased to a large extent.