The main purpose of the present work is to study the role of Al in grain-oriented 3% Si-Fe, containing certain N contents (about 0.007%). Based on the experimental results and some thermodynamic considerations about solution-dissolution of AlN and MnS, a mechanism about the effect of Al on the magnetic properties of grain-oriented 3% Si-Fe is proposed, according to which the role of Al is to form AlN, as effective inhibitors.