The purpose of this study was to determine if there are changes between preoperative and postoperative somatosensory evoked potentials(SEP) in patients with low back pain who underwent surgery and if the changes of SEP and symptom improvement correlate. 40 patients who had low back pain and underwent surgery for lumbosacral disc herniation or spinal stenosis verified by magnetic resonance image were studied. In preoperative examination, physical examination(including straight leg raising, motor and sensory examination, deep tendon reflexes), SEP were done. Postoperative examinations were done in postoperative 1 week and 1 month. In postoperative 1 week SEP study there were no changes in 23 patients, improvement in 8 patients and aggravation in 4 patients(odds ratio=2, confidence interval 0.15∼0.6). In postoperative 1 month SEP study there were no changes in 10 patients, improvement in 11 patients and aggravation in 1 patient(odds ratio=8.33, confidence interval 0.012∼0.705). There was significant improvement in SEP after the operation in preoperative 1 week and in 1 month. There was no significant correlation between symptom improvement and improvement of SEP(P=0.507) but in patients with symptomatic improvement, there was improving tendency of SEP. Further study would be necessary with more cases.