The idea of sending massages from one person to another is a tradition that is as old as man in history. With the development of the art of writing, Arabic language played and still plays an important role in communication as a medium of expression. In most of the West African empires, Arabic served as the official language of administration. For instance, in old Ghana Empire, Mali, Songhay, and Kanem-Borno, the role of Arabic was very prominent. In the Sokoto Caliphate, it was a language of administration used for keeping records and documents. More importantly, it was a language of literacy, civilization and cultural attainment of the period. This paper discusses Arabic language as a source of diplomatic relations between the Sokoto Caliphate and its neighbours. In doing this, we began by looking at the historical foundation of Sokoto Caliphate. We then discussed the historical background of Arabic and literary works of some scholars. In the second part of the paper, we looked at the role of Arabic language in the official correspondence within the Sokoto Caliphate on one hand and between the Sokoto Caliphate and its neighbours on the other hand. The third part of this paper focused on the official correspondence, the probable dates and location of the letters with examples.