Microencapsulated red phosphorus (MRP)-filled polypropylene (PP) composites were prepared using a twin-screw extruder. The effects of load and temperature as well as the dispersion or distribution of the filler particles in the matrix on the melt volume flow rate (MVR) and melt density (_m) of the PP/MRP composites were investigated using a melt flow indexer and a scanning electron microscope. The temperatures and loads were varied from 180 to 205°C and from 2.16 to 12.5 kg, respectively. The results showed that the MVR of the composites increased nonlinearly with increase in temperature and load. The sensitivity of MVR of the composite melts to temperature was significant. The MVR of the composites also decreased slightly with an increase in the MRP weight fraction. However, the values of _m of the composites varied slightly with increase in load, temperature, and MRP weight fraction. The findings can provide useful information for optimum processing of these composites.