In the title compound, C(17)H(14)O(5)S, the coumarin ring system is nearly planar, with a maximum deviation of 0.034 (2) Å from the mean plane. The dihedral angle between the benzene ring and the coumarin ring system is 56.11 (6)°. The crystal packing is stabilized by C-H⋯O hydrogen bonding, which forms a three-dimensional framework.