In the title compound, C21H17N3O3S, the non-H atoms, apart from those in the benzoyl group, are almost coplanar (r.m.s. deviation = 0.049 Å) and the benzoyl group is almost orthogonal to the plane of the rest of the molecule [dihedral angle = 80.34 (6)°]. In the crystal, a combination of N—H...O and asymmetric bifurcated O—H...(N,O) hydrogen bonds link the molecules into a three-dimensional network. Weak C—H...O interactions are also observed.