Vicat softening point temperature (T-V) and heat deflection temperature (T-d) are important parameters for characterization of heat resistant properties of polymeric materials. PP/Al(OH)(3)/Mg(OH)(2) flame retardant composites were prepared using a twin-screw extruder, and the T-V and T-d of the composites were measured. The results showed that the T-V and T-d increased nonlinearly with an addition of the weight percentage of the flame retardant additives except for individual data points, while the T-V and T-d decreased with increasing the filler particle size when the content of flame retardant additives was constant. Under the same conditions, filling small amount of zinc borate into the composites might improve the heat resistant properties of the composite systems. Moreover, the morphology of the impact fracture surface of the specimens was observed by means of scanning electron microscope to understand the dispersion and distribution of the filler particles in the PP matrix.