Abstract: Halloysite nanotubes (HNTs) were compounded with 2-carboxyethyl phenylphosphonic acid (CEPPA) and used for modification of epoxy (EP) to prepare CEPPA-HNTs/EP composite. The effects of the ratios of CEPPA and HNTs on the thermal stability, flame retardancy and mechanical properties of the CEPPA-HNTs/EP composite were studied. TG analysis shows that the combination of CEPPA and HNTs can improve the thermal stability of the CEPPA-HNTs/EP composites, promote the carbonization and reduce the decomposition rate. The analyses of cone and limiting oxygen index show that adding HNTs can reduce the heat release rate, while CEPPA has a more significant effect on the increasing of oxygen index. The FTIR and SEM of the carbon residue show that the reaction of CEPPA and HNTs during the combustion produce silica-aluminate, which promotes the dehydration and cross-linking of the condensed phase. The analysis of mechanical properties shows that when mass ratio of HNTs to EP is 6%, mass ratio of CEPPA to EP is 4%, the tensile strength and impact strength of CEPPA-HNTs/EP composite are increased by 19.4% and 17.3%, respectively. SEM morphologies of impact sections of CEPPA-HNTs/EP composite show the characteristics of ductile fracture.