The(E)and(Z)-isomers of the title compounds were prepared from the reaction of 3-acetyl-7-methoxy-N-phenyl-1,2-dihydrocinnoline 1,2-dicarboximide and O-methylhydroxylamine hydrochloride and the structureswere characterized by X-ray diffraction. The(E)-isomer crystallizes in monoclinic, space group P21/cwith cell parameters of a = 12.168(3)Å, b = 14.908(3)Å, c = 13.258(3)Å, β= 114.65(1)°, and Z = 4 ;the final residual factor is R1 = 0.063 for 2677 reflections. The(Z)-isomer crystallizes in monoclinic, spacegroup P21/c with cell parameters of a = 10.867(4)Å, b = 13.507(2)Å, c = 15.170(3)Å, β= 106.63(2)°,and Z = 4 ; the final residual factor is R1 = 0.055 for 3176 reflections.