This paper presents the effects of electron irradiation on the characteristics of single mode optical fibers doped with rare earth Er3+. The parameters of optical fibers are measured, prior to irradiation and after irradiation and annealing. It has been found that absorption loss in the wave length range of 0.80-1.60 μm is greatly lager than those of unirradiationed fibers. The irradiation induced loss obeys the following exponential laws: LUV =0.342exp E(eV)/0.166 in the range of 0.80-1.20 urn and LIR = 2.2×104exp -6.08E(eV) in the range of 1.20-1.60 μm range. During annealing, the induced loss at longer wave length decreases, but that near 0.80 μm increases. Finally, the paper discusses the mechanism of loss variations. The displaced probability of oxygen and silicon atoms in electron irradiation is estimated to be 7.1×10-8 and 3.9×l0-8, respectively. The loss induced by displaced atoms is 200 times langer than that induced by the same amount of OH- at 1.40 μm. The process of annealing of the loss essentially occurs in two steps, i.e., by neutralization of the free electron and reforming of the broken bonds.