A class of oxalic diamides are found to be effective ligands for promoting CuI-catalyzed aryl amination with less reactive (hetero)aryl chlorides. The reaction proceeds at 120 degrees C with K3PO4 as the base in DMSO to afford a wide range of (hetero)aryl amines in good to excellent yields. The bis(N-aryl) substituted oxalamides are superior ligands to N-aryl-N'-alkyl substituted or bis(N-alkyl) substituted oxalamides. Both the electronic nature and the steric property of the aromatic rings in ligands are important for their efficiency.