The present invention provides an optical semiconductor sealing material comprising a radically polymerized polymer of a methacrylate ester having an alicyclic hydrocarbon group containing 7 or more carbon atoms e.g. an adamantyl group, a norbornyl group or a dicyclopentanyl group; and an optical semiconductor sealing material comprising a radically polymerized polymer of 50 to 97 mass % of the methacrylate ester and 3 to 50 mass % of acrylate ester having a hydroxyl group. The optical semiconductor sealing material of the present invention is highly transparent and stable to UV light and thus does not undergo yellowing. In addition, the material exhibits excellent compatibility between heat resistance and refractive index, does not undergo deformation or cracking during heating processes such as reflow soldering, and shows high processability. The material can be preferably used as a sealing material for light-emitting elements and light-receiving elements of optical semiconductor devices (semiconductor light-emitting devices).