Irradiation effects on optical fibers were observed with 14 MeV fusion neutron and fission neutron. As a result, the following characteristics have become clear. Permanent absorption loss after fission and fusion neutron irradiation, were greater than that of gamma ray irradiation. In case of fission neutron, large absorption loss appeared at wavelength of shorter than 700 nm and loss peak of 600 nm, and absorption loss increased exponentialy to the fluence of 10^ n/cm^2. During irradiation, the light emission was observed in the wavelength of 400 to 1700 nm and peak of light at about 1200 nm was appeared. Two kinds of the SiO_2 fibers were survived irradiated up to 3 x 10^ n/cm^2
