In this study, polyurethane (PU) composites were produced with the addition of 2, 4-ditert-butylphenyl phosphite (FR) as a fire-retardant, with loading percentage of 0, 2, 4, and 6% by weight to palm-based ester resin.Its effect on the mechanical (hardness, impact and flexural strength and modulus) and thermal properties (thermal stability and fnre test) of the PU composites were studied.It was observed that the Shore D hardness increased marginally with increasing FR content, where higher loading of FR led to higher hardness (up to 38%).The impact and flexural strengths decreased with increasing FR loading attributed to the weak interfacial bonding between the FR and the PU matrix.The impact strength decreased by 25%, 24% and 23% from 2 to 4 and to 6% FR loading respectively.