In the title compound, C(21)H(16)N(2)O(3)S, the central quinazolin-4-one ring is planar (r.m.s. deviation = 0.037 Å). The N-bound benzene and thio-phenyl rings are almost perpendicular to the central plane [dihedral angles = 82.22 (5) and 77.05 (13)°, respectively]. Mol-ecules are connected into a three-dimensional array by C-H⋯O inter-actions involving both carbonyl O atoms. The thio-phene ring is disordered over two positions, which are approximately parallel and oppositely orientated. The major component refined to a site-occupancy factor of 0.6555 (17).