Abstract： Objective To evaluate the midterm efficacy of prosthetic disc nucleus ( PDN) replacement for the treatment of lumbar disc herniation. Methods Twenty cases of lumbar disc herniation( including one case of recurrent lumbar disc herniation) were treated with PDN. The twenty cases were followed-up 5.4 ～6.2 years( mean 5.7 years). Functional,and radiographic follow-up examinations,MRI and follow-up records of all patients were reviewed carefully. Results Clinical evaluation at the end of follow-up,there were 10 cases in excellent,6 cases in good,2 cases in fair and 2 cases in poor,and good rate was 80%. One patient accepted the revision operation to remove the PDN because of device migration. One patient accepted the fusion because of adjacent segment disease. The others experienced pain relief, and resumed their normal life and work. The average Oswestry score and VAS get better significantly. Conclusion The PDN was effective in treating patients with lumbar disc herniation. However, the medium term complications of device subsidence should be taken seriously.