PURPOSE: To obtain the subject composition little in coloration, good in thermal stability, and useful as a material for various containers by adding a specific metal compound to a resin containing methacrylonitrile as a main component.

CONSTITUTION: This resin composition comprises a resin produced by polymerizing (A) methacrylonitrile alone or copolymerizing the component A with one or more monomers of an aromatic vinylic compound, a (meth)acrylate ester and a vinyl cyanide compound which can be copolymerized with the component A, and (C) a metal compound of the formula (M is Al, Mg; (n) is 1-3; (m) is 0-3; R is the residue of a surfactant). Therein, the content of the component A is ≥60wt.%, and the content of the component C is 50-2000ppm in terms of the metal. This composition is preferably obtained by polymerizing 100 pts.wt. of the whole monomers of component A or the components A and B in the presence of 1-30 pts.wt. of a rubbery polymer with a carboxylic acid type metal salt and subsequently salting out the product with an electrolyte aqueous solution having a pH of 1-8.