In the title compound, C(10)H(12)ClN(3)OS, the -C=N-N-C- chain bridging the ethyl-imino group and the benzene ring adopts an extended conformation with a C-N-N-C torsion angle of -171.98 (11)°. The imino H atom of the chain is a hydrogen-bond donor to the S atom of an inversion-related mol-ecule, forming a supra-molecular dimer. The hy-droxy H atom is intra-molecularly hydrogen bonded to the azomethine N atom.