A novel ortho-amide functional benzoxazine monomer containing acetylene group has been synthesized in this study. The chemical structures of synthesized monomer are confirmed by H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The polymerization behaviors including both ring-opening polymerization of oxazine ring and polymerization of acetylene functionality are investigated by in situ FTIR and differential scanning calorimetry (DSC). The activation energy of polymerization has also been studied, and the activation energy of the polymerization is determined to be 104.4 kJ/mol and 103.1 kJ/mol, respectively, according to Kissinger and Straink methods. In addition, the benzoxazole formation during the thermal treatments is analyzed by solid state C-13 NMR. The resulting thermoset derived from benzoxazine monomer exhibits excellent thermal stability and low dielectric constant, indicating its potential applications in aerospace, electronics industries and other composite areas requiring high performance polymeric matrix.