A nickel-catalyzed cycloaddition of aromatic (O-benzyl)ketoximes with alkynes to afford 3,4-disubstituted isoquinoline derivatives has been developed. The reaction involves oxidative addition of N-O bond of O-benzylketoxime to Ni(0) and subsequent intermolecular C-H bond activation via elimination of benzyl alcohol. It was also found that ketoximes participate in the nickel-catalyzed reaction with alkynes to furnish isoquinoline N-oxide derivatives.