Abstract: To meet the growing demand for high-temperature-resistant, low-dielectric-constant resins in electrical insulation applications, an alicyclic epoxy resin (EP) was selected as the matrix. Exploiting the copolymerization reactivity between benzoxazine and epoxy resin, a methylamine-based benzoxazine resin (BA) was used to modify EP. A series of EP/BA systems were prepared via melt blending followed by stepwise curing. An EP/anhydride system was used as a reference for comparison. The curing behaviour and thermal properties of the resin systems were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). In parallel, dielectric properties, breakdown strength, water absorption, and flexural properties were evaluated. Results show that the incorporation of BA decreases the onset curing temperature of the modified system. The curing proceeds through sequential reactions: ring-opening self-polymerization of benzoxazine, followed by copolymerization between benzoxazine and epoxy, leading to a synergistic benzoxazine-epoxy crosslinked network. With increasing BA content, the glass transition temperature (T_g) increased and reached a maximum of 249.6 ℃, which is higher than that of neat epoxy resin. The dielectric constant decreased to a minimum of 2.75, the breakdown strength peaked at 58.01 kV/mm, the 30 d water absorption decreased to 1.42%, and the flexural strength reached 91.9 MPa. Overall, the properties of the PEP/BA system are superior to the EP/anhydride system. This modified epoxy resin combines excellent thermal stability and electrical insulation performance, offers controllable cost, and can be readily prepared, showing promising potential for insulation applications.