Objective To investigate the effects of 17β-estradiol on the cell apoptosis after chronic spinal cord injury in ovariectomized rats. Methods A total of 90 female Wistar rats (weighing, 220-250 g) received removal of bilateral ovaries. After 2 weeks, the rats were randomly divided into 3 groups (n=30): sham-operation group (group A); chronic gradual spinal cord injury model and 17β-estradiol treatment group (group B); and chronic gradual spinal cord injury model and normal saline treatment group (group C). Rats of group A only received removal of spinous process at T10. Rats of groups B and C were made the models of chronic gradual spinal cord injury, and then 17β-estradiol (100 μg/kg, twice a week) and normal saline were given by peritoneal injection, respectively. The cell apoptosis and positive cells of Caspase-3 were examined by the TUNEL methods and Caspase-3 immunohistochemical staining at 1, 3, 7, 14, 28, and 60 days after modeling; and the neurological function was evaluated by Tarlov scale and inclined plane test scoring. Results At 14, 28, and 60 days after modeling, Tarlov scale and inclined plane test scores of group B were significantly better than those of group C (P lt; 0.05), but were significantly lower than those of group A (P lt; 0.05). At 28 days after modeling, HE staining showed that the edema of spinal gray matter and the neurons, the proliferation of glial cells and astrocytes, and less pathologic change were observed in group B; and the pathological changes in group B were mitigated than in group C. At 60 days after modeling, edema of spinal gray matter and the neurons was significantly ameliorated in group B. At 14, 28, and 60 days after modeling, the rate of Caspase-3 positive cells in group B was significantly lower than in group C (P lt; 0.05), but was significantly higher than in group A (P lt; 0.05). At 7, 14, 28, and 60 days after modeling, the cell apoptotic rate was significantly lower in group B than in group C (P lt; 0.05), but was significantly higher than in group A (P lt; 0.05). Conclusion 17β-estradiol can reduce the numbers of apoptotic cells and promote the nerve function recovery after chronic spinal cord injury of rats.