A novel compound (bis(3-hydroxyaminophenyl) phenyl phosphine oxide) (BHAPPO) was synthesized as a flame retardant based on bisphosphoramide structure. Rigid polyurethane foam (RPUF) formulations were prepared with different BHAPPO and ammonium polyphosphate (APP) content to investigate both flame retardant property of BHAPPO and the possible synergistic effect of BHAPPO and APP against RPUFs. FT-IR, 1H-NMR and 31P-NMR spectroscopy analysis confirmed the expected structure of BHAPPO. Flame retardancy and thermal degradation behavior of RPUFs were determined by limiting oxygen index (LOI) test and thermogravimetric analysis (TGA). The flame retardant property of novel BHAPPO against the prepared RPUF samples was confirmed. The synergetic effect of BHAPPO and APP combination both on reducing the flammability and enhancing the char formation of RPUFs was also confirmed with a dependence on their ratio. The compatibility effect of BHAPPO on mechanical and morphological properties of RPUFs was also investigated by compression test and SEM analysis. Fire behaviors and the effect of using flame retardant additives in polyurethane foam were investigated using a cone calorimeter. Carbon dioxide amount was found lower for flame retardant PU foam.