Aromatic polyamides were prepared from various diacids with a new diamine bearing two 9,10-dihydro-9-oxa-10-oxide-10-phosphaphenanthrene-10-yl (DOPO) substituents. The polyamides possessed inherent viscosities of 0.33–0.81 dl/g and glass transition temperatures of 230–251 °C measured with DSC. All the polyamides were amorphous and readily soluble in NMP, DMAc, DMF, and DMSO. Incorporating DOPO groups into polyamides resulted in polymers with low initial decomposition temperatures (IDT, 310–362 °C), deriving from the decomposition of the DOPO groups. With thermogravimetric analysis (TGA), the DOPO-containing polyamides exhibited high integral procedure decomposition temperatures (IPDT) of 928–1086 °C, to indicate improvement on polyamides' weight loss rate, thermal stability, and heat insulating property at high temperature region. High tensile strength of 42.0–52.8 MPa and Young's modulus of 506–869 MPa measured with stress–strain tests were observed for the polyamides to indicate these polymers possessing good mechanical properties. ; JNL0002565