A novel derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) bearing cyano groups, referred to as PDPO, was successfully synthesized and applied as an additive for epoxy resin (E-44, with epoxide equivalent weights ranging from 201 to 240 g/epoxide), along with the curing agent 4,4′-diaminodiphenylmethane (DDM). Comprehensive characterization techniques, including Fourier transform infrared (FTIR) spectroscopy, 1H and 31P nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis (EA), were employed to confirm the chemical structure of PDPO.