In the present study, we examined change of ionized calcium-binding adapter molecule 1 (Iba-1) in the adult and aged gerbil spinal cords. Significant change of morphological feature and neuronal cell loss were not observed in both adult and aged spinal cords of gerbil after NeuN immunohistochemistry and Fluoro-Jade B histofluoresce staining. Iba-1–immunoreactive microglia broadly distributed in the spinal cord. Most of Iba-1–immunoreactive microglia showed ramified forms in the adult gerbil cervical and lumbar spinal cords. However, morphological changes of Iba-1–immunoreactive microglia were observed in the cervical and lumbar regions of the aged gerbil spinal cord. These microglia were showed a hypertrophied body with shortened swollen processes which was characteristic of activated microglia. In addition, Iba-1 protein level significantly higher in aged cervical and lumbar spinal cords than those in the adult gerbil. The present study showed an increase of activated forms of Iba-1–immunoreactive microglia and its protein level without marked changes in morphological features and neuronal loss in the aged spinal cord compared to those in the adult gerbil spinal cord. This result suggests that the increase of Iba-1 expression in the aged spinal cord may be closely associated with age-related changes in aged gerbil spinal cord.