A high-polymer neutron shielding material which scarcely reduces the hydrogen number density when exposed to a high temperature of 150 to 200°C for a long time period A heat-setting type epoxy resin is employed. The base resin is selected from various epoxy resins such as bisphenol A type epoxy resin. The hardener is selected from alicyclic polyamine, polyamide amine, aromatic polyamine, acid anhydride, and so on. These materials are mixed and hardened at a temperature higher than the room temperature. To give a flame resistance to the hardened resin, a fire retardant such as magnesium hydroxide is added to the mixture. To improve the neutron shielding performance of the hardened resin, a neutron absorbing material is added to the mixture. Further, to increase the moderating performance, hydrogenated bisphenol A epoxy resin is used as the base resin or metal hydride or hydrogen absorbing alloy is added. The present neutron shielding material works as a significant neutron shielding material as its hydrogen number density does not go down for a long time under a high-temperature condition and the neutron shielding performance does not go down.