A novel sulfonic acid-containing benzoxazine monomer, 3-[4-(4-(6-sulfo-3,4-dihydro-2H-1,3-benzoxazine-3-yl)benzyl)phenyl]-3,4-dihydro-2H-1,3-benzoxazine-6-sulfonic acid (abbreviated as SHS-ddm), was synthesized via Mannich reaction and acidizing reaction using sodium 4-hydroxybenzenesulfonate, 4,4'-diaminodiphenylmethane, and paraformaldehyde as raw materials. The structure of SHS-ddm was characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (H-1 NMR) spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The crosslinked sulfonic acid-containing polybenzoxazine [poly(SHS-ddm)] membrane was prepared through high temperature solutioncasting method. Membrane properties including proton conductivity, methanol permeability, mechanical property, hydrolytic and oxidative stabilities were evaluated in detail. Our results showed that poly(SHS-ddm) membrane exhibited a high proton conductivity of 0.154 S cm(-1) at 80 degrees C and a very low methanol permeability of 5.8 x 10(-8) cm(2) s(-1). The calculated selectivity parameter was 2.655 x 10(6) S s cm(-3), which was much higher than that of Nafion 117 (8.081 x 10(4) S s cm(-3)). Employing this membrane in the membrane-electrode assembly (MEA), high methanol concentration up to 7 M was used. The cell exhibited a stable open circuit voltage (V-OC) of 0.76 V and a maximum power density of 66.5 mW cm(-2). Accordingly, only relatively low voltage drop of 1.415 mV h(-1) was observed after a continuous operation for 12 h. Overall, this novel polybenzoxazine exhibited special potential for proton exchange membrane with low methanol permeability and low cost in direct methanol fuel cells.