Disclosed is a thermoplastic resin composition contains including a methacrylic resin having a ring structure in a main chain thereof and a glass transition temperature of 110° C. or higher, and at least one kind of metal compound selected from metal salts, metal complexes, and metal oxides, wherein a content of the metal compound in the composition is from 10 to 10,000 ppm in terms of metal atom based on a mass of the methacrylic resin, and a process for producing such a thermoplastic resin composition, the process including carrying out, when preparing a methacrylic resin having a ring structure in a main chain thereof and a glass transition temperature of 110° C. or higher, cyclization condensation reaction using a catalyst to form the ring structure; and then adding a deactivator of the catalyst.