In the title compound, C(11)H(10)ClN(3)O, the quinoline ring system is essentially planar, the r.m.s. deviation for the non-H atoms being 0.014 (2) Å with a maximum deviation from the mean plane of 0.0206 (14) Å for the C atom bonded to the -CH-N=NH(2) group. In the crystal, molecules are linked via N-H⋯O and N-H⋯N hydrogen bonds, forming zigzag layers parallel to (010).