One of the significant events of the beginning of the reign of Tukultī-Ninurta I (c. 1242-1206 BC), one of the most powerful rulers of the Middle Assyrian period, was the victorious military campaign against the "the lands of Nairi (KUR.KUR. Na-i-ri)". We dis-cuss this event in the context of the expansionist policy of Tukultī-Ninurta I in the north-western direction in the first three years of his reign. The study of these inscriptions of Tukultī-Ninurta I clearly shows that c. 1240/39 BC, after the invasion of the rebellious Šubarû, Alzi, Amadanu and the surrounding areas, the borders of Assyrian rule reached the Taurus Mountains, beyond which were "the lands of Nairi ". Although in his inscription Tukulti-Ninurta I called Nairi "an unknown land (Na-i-ri ana KUR la i-du-ú)", nevertheless, it is quite possible that Nairi was one of the participants in the anti-Assyrian alliance and played a certain role in Alzian uprising against Šulmānu-ašarêd (Shalmaneser) I (c. 1272-1243 BC). It is likely that Nairi's anti-Assyrian position was due to the desire to control the Taurus passes and the transformation of Alzi into a safe zone against the Assyrian attacks. The fact of the consolidation of the "Kings of 40 lands" of the "Nairian" camp hostile to Assyria indicates that the ruling Nairian circles had time to unite their forces against Assyria. The study of inscriptions on military campaigns and constructions in the first three years of the reign of Tukultī-Ninurta I suggests that he invaded the "lands of Nairi" in the fourth year of his reign, i.e. c. 1239/1238 BC.