The purpose of this research is to show the fight of Pope Adrian I against the Adoptionist heresy in his correspondence with the Spanish bishops. Abbot Beatus and Bishop Etherius, the main opponents of the adoptionist heresy in Spain, inform Pope Adrian about the dogmatic problem that has arisen in the Spanish Church. The Archbishop of Toledo, Elipand, presented the teaching that Jesus Christ is the Son of God by nature, and as a man, he is the Son of God by adoption. Pope Adrian wrote two letters to the Spanish episcopate against adoptionist heresy and was one of the first fighters against adoptionism in the Church in the West, not taking into account the territory of the Iberian Peninsula and the actions of Elipand’s opponents in Spain. His correspondence with the Church in Spain will be analyzed in a broader historical context and should help us understand the theological-historical relations between Rome, the Church in Spain, and the Frankish Church and state in the last quarter of the VIII century. This paper aims to analyze the letters of Pope Adrian to gain insight into the arguments used by the Pope to prove the correctness of his theological views, and on the other hand, that the teachings of his opponents are not in line with the teachings of the Orthodox Church and to see the Pope’s contribution in the fight against Adoptionism.