A resin composition is a transparent, low-water-absorption polyolefin-based resin composition containing a sorbitol-based derivative of a particular structure, whose polyolefin-based resin having crystallinity of 0% to 20% shows haze of not more than 10%, total light transmittance of not less than 80%, when measured in accordance with ASTM D1003 using an article 3 mm thick molded therefrom as the test specimen, and shows water absorption of not more than 0.1% after 100-hour immersion in water at 23.degree. C., or whose polyolefin-based resin comprises a cyclic olefin-based polymer comprising a cyclic olefin of a particular structure. Preferable examples of the polyolefin-based resin include the aforesaid cyclic olefin-based polymer and a polycyclohexane-based resin. This resin composition is used for transparent resin moldings that are useful as optical products and moldings for medical and pharmaceutical use because it has excellent transparency, heat resistance, rigidity and water vapor resistance and the decline in its transparency in a high-temperature/high-humidity atmosphere will be little.