Process for the production of expanded particles of a polypropylene resin

In a process for the production of expanded particles, wherein an aqueous dispersion comprising polypropylene resin particles containing a blowing agent and an aqueous medium, and maintained within a closed vessel under pressure and at a temperature higher than the softening point of the polypropylene resin particles, is released from one end of the vessel into an atmosphere maintained at a pressure lower than that within the vessel to expand the polypropylene resin particles, the improvement comprising said polypropylene resin particles which contain an expansion aid having a particle size of 0.1 to 150 .mu.m and a melting point higher than said temperature at which said aqueous dispersion is maintained, in an amount of 0.05 to 2% based on the weight of the polypropylene resin particles, said expansion aid being an organic, crystal nucleus material or an inorganic material selected from the group consisting of aluminum hydroxide, calcium hydroxide, magnesium hydroxide, magnesium carbonate, barium carbonate, calcium sulfite, magnesium sulfite, calcium sulfate, magnesium sulfate, aluminum sulfate, calcium oxide, kaolin and zeolite.