A natural component, sesamin (SA), was used to replace conventional amine as co-initiator for dental composite. A combination of camphorquinone (CQ) and SA was employed to initiate the photopolymerization of 2-2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl] propane/triethylene glycol dimethacrylate (70/30 wt.%). The kinetics was recorded by real-time Fourier transform infrared spectroscopy. The mechanical properties were measured by dynamic mechanical analysis, the cell toxicity was investigated by MTT assay and a mixture of CQ and ethyl 4-N,N-dimethylaminobenzoate (EDMAB) was used as control in the same photocuring condition. The results indicated that the addition of SA as co-initiator greatly improved the rate of polymerization and final double-bond conversion (DC) when compared with the system initiated by CQ alone. Compared with EDMAB, the final DC of the CQ/SA system (71%) was slightly lower than that of CQ/EDMAB (76%); SA resulted in approximately the same storage modulus at around 37 Β°C, but a slightly higher glass transition temperature. SA produced lower yellowing effect and good in vitro biocompatibility. The water sorption and solubility for two mixtures were very close and within the range of the ISO 4049 specification. These results suggest that SA is an effective alternative co-initiator to conventional amine. The natural compound characteristics of SA make it more promising than amine in dental resin formulations.