A method for producing styrene-modified polyethylene-based resin beads, including the steps of: dispersing 100 parts by weight of polyethylene-based resin beads which contain an inorganic nucleating agent and have a melting point of 95° C. to 115° C., 20 parts by weight or more and less than 300 parts by weight of a styrene-based monomer and a polymerization initiator into an aqueous suspension containing a dispersant; impregnating the polyethylene-based resin beads with the styrene-based monomer under heating the resulting dispersion at such a temperature that the styrene-based monomer does not substantially polymerize; and performing polymerization of the styrene-based monomer at a temperature of (T)° C. to (T+25)° C. (where T° C. is a melting point of the polyethylene-based resin beads.)