Objective To investigate the effect of telomerase activation on biological behaviors of neural stem cells after hypoxic-ischemic insults. Methods The neural stem cells passaged in vitro were divided into four groups: control, oxygen-glucose deprivation (OGD), OGD+cycloastragenol (CAG) high concentration (final concentration of 25 μM), and OGD+CAG low concentration (final concentration of 10 μM). The latter three groups were subjected to OGD. Telomerase reverse transcriptase (TERT) expression level was evaluated by Western blot. Telomerase activity was detected by telomerase repeat amplification protocol (TRAP). Cell number and neural sphere diameter were measured under a microscope. The activity of lactate dehydrogenase (LDH) was examined by chemiluminescence. Cell proliferation rate and apoptosis were detected by flow cytometry. Results After OGD insults, obvious injury of neural stem cells was observed, including less cell number, smaller neural sphere, more dead cells, lower proliferation rate and decreased survival rate. In CAG-treated groups, there were higher TERT expression level and telomerase activity compared with the control group (P < 0.05). In comparison with the OGD group, CAG treatment attenuated cell loss (P < 0.05) and neural sphere diameter decrease (P < 0.05), promoted cell proliferation (P < 0.05), and increased cell survival rate (P < 0.05). Low and high concentrations of CAG had similar effects on proliferation and survival of neural stem cells (P > 0.05). In the normal cultural condition, CAG treatment also enhanced TERT expression (P < 0.05) and increased cell numbers (P < 0.05) and neural sphere diameter (P < 0.05) compared with the control group. Conclusions Telomerase activation can promote the proliferation and improve survival of neural stem cells under the state of hypoxic-ischemic insults, suggesting telomerase activators might be potential agents for the therapy of hypoxic-ischemic brain injury.