The aim of the research is to reveal the contribution of Kitab al-'Ayn, which is considered a milestone in its field as a dictionary and attributed to al-Khalīl ibn Aḥmad alFarāhīdī (d. 175/791), to Arabic grammar as a field other than lexicography. By scanning the aforementioned work, the grammatical subjects it contains have been determined. The contribution of Kitab al-'Ayn to grammar has been revealed by evaluating and comparing the obtained determinations and the quotations made by other Arabic language authors to these determinations. At the beginning of these authors, Abu Bishr Amr ibn Uthman Sibawayh (d. 180/796) and his work al-Kitāb. In the research carried out with the qualitative method, the references made by the linguists of the Basra and Kufe language school, who lived in the first three centuries of Hijra, to these two works, primarily Kitab al-'Ayn, were taken as a basis. The specified time period is the virgin and original period, in which the Arabic grammar was processed most intensively, and it was the source of the following periods. In addition, in the relevant period, members of other language schools were not mentioned, as their formation was not fully realized and they were devoted to independent research. On the other hand, the grammatical contents of Kitab al-'Ayn, which has much more than what is mentioned in the research, are included in the works in the relevant time period in accordance with the purpose. Thus, over the Kitab al-'Ayn sampling; In addition to examining the Arabic vocabulary or lexicon of such works, which were generally called dictionaries or mu'cem at that time, "does it also include grammar topics?" the positive answer to this question was confirmed.