Monofunctional benzoxazine with para-methylol functionality has been synthesized via Mannich condensation. The chemical structure of the synthesized monomer is confirmed by H-1 nuclear magnetic resonance (NMR), C-13 NMR and Fourier transform infrared spectroscopy (FT-IR). Polymerizations are monitored by in situ FT-IR, H-1 NMR and differential scanning calorimetry (DSC). Activation energy of the polymerization is also studied by DSC. The apparent activation energy of the polymerization is calculated to be 79.8 kJ mol(-1) and 81.5 kJ mol(-1) according to the Kissinger and Ozawa methods, respectively. In addition, thermogravimetric analysis (TGA) result shows that the polybenzoxazine derived from para-methylol functional benzoxazine possesses excellent thermal stability with an initial decomposition temperature of 395 degrees C for a 5% weight loss and a char yield of 60% at 800 degrees C under N-2.