2, 2-Bis [4- (2-hydroxy-3-methacryloyloxypropoxy) phenyl] propane (bis-GMA) is widely used in dentistry as a monomer of composite resin system and their bonding agents. Since bis-GMA is not purified, its isomers and some chemicals such as residual initiator remain in the commercial product. Bis-GMA and iso-bis-GMA were separated from bis-GMA monomer by HPLC. NMR spectra of both monomers were recorded, and their all signals in 1H and 13C-NMR spectra were assigned using DEPT and COSY experiments.