The title compound, 3-(4-methoxy-benzylidene)-isothiochroman-4-one (C17H14O2S) was prepared from the reaction of isothiochroman-4-one with benzaldehyde in the presence of small amount of HCl. The structure of the synthesised compound was determined by IR, H-1 NMR and X-ray crystallography. The structure was solved in monoclinic, space group P2(1)/n with a = 3.9773 (7) a"<<, b = 10.918 (2) a"<<, c = 30.609 (6) a"<<, beta = 90.615 (3)A degrees, V = 1329.1 (4) a"<<(3), Z = 4 and with R (int) = 0.047. The bicyclic ring of isothiochroman-4-one moiety does not adopt a planar geometry. The molecular conformation is stable via C10-H center dot center dot center dot O1 and C16-H center dot center dot center dot S1 intramolecular hydrogen-bonding interactions. These contacts involve molecules in an extended two-dimensional sheet to the bc plane.