PURPOSE: To provide a high quality nitrile by reacting boron compounds, which is hardly removed, with alcohol and recovering the nitrile by distillation.

CONSTITUTION: By adding an alcohol selected from the group comprising aminoalcohol and glycol containing (a) at least two OH groups or (b) an NH2, an NHR group or an NR2 group wherein R represents methyl or ethyl, and an OH group (e.g. triethanolamine or ethyleneglycol) to a reaction mixture containing adiponitrile obtained by reacting butadiene with hydrogen cyanate using a nickel catalyst and a boron compound as a promoter a 2- methylglutaronitrile and boron residue, recovering nitrile by distillation and removing an organic boron compound the high quality nitrile is provided, which can provide diamine in a high yields by hydrogenation and reduce the amount of undesired side products such as benzene produced by pyrolysis of boron contamination.