Abstract: A novel high-melting-point phosphazene derivative, hexa(p-methylbenzamidephenoxy)cyclotriphosphazene (HBPCP), was designed and synthesized in this work. The goal is to address the inherent flammability of dicyclopentadiene phenol epoxy resin (EP) and the limitations of conventional phosphazene flame retardants-such as hexa phenoxy cyclotriphosphazene (HPCP)-which suffer from poor thermal stability and processing-related migration. The HBPCP was synthesized through a three-step process-nucleophilic substitution, oxidation, and acylation-amidation-with overall yields ranging from 89% to 95%. HBPCP remains solid at the EP processing temperature (185℃), effectively preventing additive migration and subsequent degradation of mechanical properties. Thermogravimetric analysis (TGA) revealed that HBPCP exhibits excellent thermal stability, with a residual char yield of 41.82% at 800℃. Moreover, flame retardancy tests showed that adding 12.5 wt% HBPCP increased the limiting oxygen index (LOI) of EP from 21.19% to 27.13%, and resulted in a UL-94 V-0 rating. Additionally, the peak heat release rate (PHRR) and total smoke production (TSP) were reduced by 49.2% and 41.8%, respectively, as compared to neat EP. In terms of mechanical performance, EP/HBPCP-5 showed a 14.6% improvement in tensile strength compared to neat EP. Even for higher loadings upon the HBPCP samples, the mechanical properties remained superior to those of the unmodified resin. Furthermore, HBPCP incorporation increased the free volume in the EP matrix, reducing both the dielectric constant (Dk) and dielectric loss (Df) at high frequencies. At 10 GHz, the dielectric constant decreased from 3.26 to 3.10, thus meeting requirements for low-dielectric electronics applications. Overall, this study provides an effective method to create high-performance epoxy resins with enhanced flame retardancy, improved mechanical properties, and low dielectric characteristics.