Three types of bisphenol S (BS) based epoxy resins prepared by reaction of BS or a mixture of BS and bisphenol A (BA) with an excess of epichlorohydrin in alkaline medium or by thermal treatment of BS with diglycidyl ether of bisphenol A (DGEBA) were analyzed by reversed-phase high-performance liquid chromatography (HPLC). Some components present in the reaction products were identified by analogy with BA based epoxies, combination of semipreparative HPLC with IR and NMR spectroscopy, and derivatization of resins with HCl or NaOH.