The use of iodine-125 (125I) in cancer treatment has been shown to relieve patients’ pain. Consid-ering dorsal root ganglia are critical for neural transmission between the peripheral and central nervous systems, we assumed that125I could be implanted into rat dorsal root ganglia to provide relief for neuropathic pain.125I seeds with different radioactivity (0, 14.8, 29.6 MBq) were im-planted separately through L4-5 and L5-6 intervertebral foramen into the vicinity of the L5 dorsal root ganglion. von Frey hair results demonstrated the mechanical pain threshold was elevated after implanting125I seeds from the high radioactivity group. Transmission electron microscopy revealed that nuclear membrane shrinkage, nucleolar margination, widespread mitochondrial swelling, partial vacuolization, lysosome increase, and partial endoplasmic reticulum dilation were visible at 1,440 hours in the low radioactivity group and at 336 hours in the high radio-activity group. Abundant nuclear membrane shrinkage, partial fuzzy nuclear membrane and endoplasmic reticulum necrosis were observed at 1,440 hours in the high radioactivity group. No signiifcant difference in combined behavioral scores was detected between preoperation and postoperation in the low and high radioactivity groups. These results suggested that the mechan-ical pain threshold was elevated after implanting125I seeds without inlfuencing motor functions of the hind limb, although cell injury was present.