Through the oxidative addition of cobalt into the N-C(O) bond of phthalimide and the subsequent decarbonylation, we describe an efficient cobalt-catalyzed intermolecular decarbonylative carboamidation of alkynes. High regioselectivities have been achieved for unsymmetrical alkynes (including aryl-alkyl or aryl-aryl) to deliver polysubstituted isoquinolones. To facilitate step economy, a three-component decarbonylative carboamidation of alkynes with phthalic anhydrides and amines has been demonstrated using the current cobalt catalysis.