Abstract: A novel composite based on a semi-aromatic polyamide (PA) reinforced by multiwall carbon nanotubes (CNTs) was prepared by a solution mixing method. PA was synthesized through a direct polycondensation between azelaic acid and bis (3-amino phenyl) phenyl phosphine oxide. The effect of the CNT addition on the thermal and flammability properties of the composite were studied by thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimetry. The temperature at which 5% weight loss occurs is increased by over 70℃ by incorporating CNTs into the PA matrix. CNTs improve the flame retardancy of PA, which is manifested by a decrease of the heat release rate and the total heat release of the composite compared with pure PA.