A cyclic aryl thioester dimer was prepared by the reaction of o phthaloyl dichloride and bis(4 mercaptophenyl) sulfide in good yield under pseudo high dilution conditions via interfacial polycondensation. The structure of the cyclic dimer was confirmed by a combination of MALDI TOF MS, FTIR, gel permeation chromatography and NMR analyses. The X ray diffraction study of the single crystal of cyclic thioester dimer obtained from two solutions reveals no severe internal strain on the cyclic structure. A cyclic aryl thioester dimer was prepared by the reaction of o phthaloyl dichloride and bis (4 mercaptophenyl) sulfide in good yield under pseudo high dilution conditions via interfacial polycondensation. The structure of the cyclic dimer was confirmed by a combination of MALDI TOF MS, FTIR , gel permeation chromatography and NMR analyzes. The X ray diffraction study of the single crystal of cyclic thioester dimer obtained from two solutions reveals no severe internal strain on the cyclic structure.