Objective To study the localization of the Rasrelated nuclear protein Ran in rat somatic cells, and to investigate its interaction with the protein associated to the cell cycle. To reveal the molecular mechanism of the cell cycle control and mitotic division. Methods Fibroblasts derived from rat skin were successfully cultured with a normal tissue culture method，and investigated the localitation and possible roles of Ran during the cell mitotic division by using laser scanning confocal microscopy, repeated three times at least. Results The results showed that Ran was localized mainly in the nucleus, except for the nucleolus, in the intermediate stage rat skin fibroblasts cell. Its density was very low in the cytoplasm. After the nuclear membrane broke down in mitochysis, Ran distributed throughout the cell, but concentrated to the mitotic spindle, the concentrated area was uniformity with the spindle; in anaphase and telephase, the concentrated area changed with the spindle, localized between the separated chromosome, but lower in other sites. After mitosis, Ran migrated into the forming nucleus. There was no special distribution for Ran under the membrane of the cell fission. Conclusion Ran has a cell cycle-dependent localization and this is consistent with its regulatory roles in nuclear import and export in rat intermediate cells, the spindle assembly correctly, the correct chromosome segregation, and the cell cycle regulation.