An ultraviolet curing liquid coating composition is disclosed which, when cured with ultraviolet light in the presence of a photoinitiator, provides a buffer coating for optical glass fiber having adequate strength at room or expected elevated temperature and stability at such elevated temperature, a high index of refraction above 1.48, and a low tensile modulus which remains low to resist microbending difficulties down to around -60.degree. C. This coating composition consists essentially of a linear polyacrylate-terminated polyurethane oligomer in admixture with a liquid linear aliphatic diacrylate in which the two acrylate groups are separated by a molecular weight of at least 400 up to about 4000, said liquid linear diacrylate providing said coating composition with a viscosity suitable for coating application.