The present invention provides a thermoplastic composition excellent in heat resistance and water resistance which comprises a thermoplastic saturated norbornene polymer which has a number-average molecular weight (Mn) of 50,000-500,000 and a weight-average molecular weight (Mw) of 100,000-2,000,000 which are measured by high performance liquid chromatography, and a molecular weight distribution (Mw/Mn) of 2.2 or more, and a volatile content of at most 0.3% by weight. The composition is suitable for optical materials, electroconductive composite materials and optical recording media.