Differences from the aspect of usul al-nahw among the schools of Arabic grammar lead to differences in grammarians’ opinions related to Arabic grammatical issues. Among those grammarians are Abu Hayyan al-Andalusiyy and Ibn Hisham al-Ansariyy. Mughni Al-Labib cAn Kutub Al-Acarib is one of Ibn Hisham’s renowned work of Arabic grammar. While Irtishaf Al-Darab Min Lisan al-cArab is considered as one of Abu Hayyan’s well-known books in the field of Arabic grammar. It is mentioned that Ibn Hisham had a lot of disagreement with Abu Hayyan. The objective of this paper is to recognize and analyse the differences between Irtishaf Al-Darab and Mughni al-Labib in their discussions related to the meaning of particle al-Lam. The particle is chosen because it has many different meanings. This article is based on a qualitative study using descriptive approach in outlining the discussions of the scholars and analysing the meanings of particle al-Lam by adopting comparative method for fair consideration and accuracy purposes. It is found that there are differences between Irtishaf al-Darab and Mughni al-Labib in the meanings of particle al-Lam. The differences are related to the meanings of al-Ikhtisas, Tawkid al-Nafy, Muwafaqah cAn, al-Tacajjub al-Mujarrad min al-Qasam, al-Tacdiyah, al-Nasab and al-Istighathah. It is hoped that the findings could be used to further describe the methodology of Ibn Hisham and Abu Hayyan in Arabic Grammar.