To clarify the role of polymerization initiator in dentin bonding, tributylborane(TBB), barbituric acid system, and BPO / amine initiators were studied for polymerization of PMMA / MMA resin at the dentin interface by FT-Raman spectroscopy. Moreover, the influences of combined use of the initiators on polymerization of the resin and dentin bonding were also examined. Polymerization at the dentin interface was promoted by TBB and barbituric acid system when dentin was treated with the conditioners effective for bonding. Initiators capable of promoting polymerization at the dentin interface tended to produce high bond strength. The combined use of TBB and barbituric acid system or BPO / amine produced desirable effects on polymerization of the resin but different effects on the bond strength depending on the combination with TBB. The combined use of BPO / amine with TBB suggested that it can improve the performance of MMA-TBB resin currently in clinical use.