Meta-phenylenediamine formaldehyde oligomer is prepared and used as an accelerator for benzoxazine resin. The structure of the oligomer is characterized by Fourier transform infrared spectroscopy and H-1 nuclear magnetic resonance spectroscopy. The molecular weight and distribution are measured by size exclusion chromatography. After mixing the accelerators with benzoxazines, the curing process of the mixtures and thermal properties, including glass transition temperature, thermal stability and char yield of the cured polymers are characterized. Comparing with the materials prepared from pristine benzoxazine and benzoxazine with molecular accelerators, usage of oligomeric accelerator is able to promote the curing and simultaneously enhance the glass transition temperature as well as thermal stability of the cured network.