PURPOSE: To facilitate extrusion molding or blow molding of PPE-based resin composition by a method wherein polyphenylene ether-based resin or specified weights of polystyrene-based resin and of specified polyvalent maleimide compound added to said resin are melt-kneaded and then blow-molded or extrusion- molded.

CONSTITUTION: Polyphenylene ether-based resin or 100 pts.wt. of polystyrene- based resin and 0.1-5 pts.wt. of polyvalent maleimide compound added to said resin are melt-kneaded and then blow-molded or extrusion-molded. The PPE- based resin used is polymer, which is obtained by oxidatively polymerizing one or more kinds of monocyclic phenols in the presence of exidative coupling catalyst and oxygen or oxygen-containing gas. On the other hand, the polyvalent maleimide compound used means organic compound having two or more maleimide groups in molecure or concretely polymaleimides represented by the general formula (1), in which R represents polyvalent organic group, X1 and X2 independently represent hydrogen atom, halogen atom or lower alkyl group, (l) is any integer more than and equal to 2 and normally any integer less than and equal to 10.