Polyurethane(PU) was mixtured by the treatment with flame retardants such as Tri(chloroisopropyl) phosphate(TCPP), Triethyl phosphate(TEP) and Trimethyl phosphate(TMP) at about . Rigid polyurethane foam was produced using the mixured products as flame retardants. The mechanical property and flammability of rigid polyurethane was investigated. The mixtured polyurethane shows reduced flammability over virgin polyurethane. Mechanical strength of mixtured polyurethane also shows as high as that of virgin polyurethane. In order to evaluate flame retardant properties of the mixtured polyurethane foams, heat release rate(HRR) of the foam was measured by cone calorimeter. Scanning electron micrograph of mixtured PU shows uniform cell morphology as virgin PU.