The reaction between 5-cholroisatin and phenylhydrazine yields the title compound, C14H10ClN3O. The molecular structure deviates slightly from the ideal planarity, with an r.m.s. deviation of 0.1372 (12) Å for the non-H atoms. An N-H...O intramolecular interaction is observed, which supports an E conformation with respect to the C=N bond. In the crystal, molecules are linked by a pair of N-H...O interactions into an inversion dimer. The dimers are linked by weak C-H...Cl interactions, formng a tape structure along [101]. The tapes are also linked through a weak [pi]-[pi] interaction [centroid-centroid distance = 3.5773 (8) Å] into a layer parallel to (-111). An in silico evaluation of the title compound with a topoisomerase enzyme was performed and the global free energy of -26.59 kJ mol-1 was found.