OBJECTIVE Although the treatment of intracranial cerebral aneurysms with detachable coils is now widely accepted, the problem of coil compaction and recanalization remains unsolved. If the vessel wall can be regenerated at the neck orifice of an aneurysm, thereby reducing the blood flow into the aneurysm, the recurrence rate of the aneurysm would decrease. Accordingly, we aimed to insert cellulose porous beads (CPBs) into rat models of external carotid artery (ECA) aneurysm and study their efficacy in promoting vessel wall regeneration. METHODS Using a rat aneurysm model, we examined the tissue response to CPBs that were inserted into the ligated ECA sac of rats. The sacs were removed on days 14, 42, 84, and 180 after insertion and subjected to conventional and immunohistochemical examination. We evaluated the tissue response in the ECA sacs and observed the vessel wall regeneration progress. RESULTS At the neck orifice of the aneurysm in which the CPB was inserted, a layer of regenerating α-smooth muscle actin-positive spindle cells was observed on day 14. The regenerative cell layer gradually thickened until day 42 and, thereafter, the thickness remained unchanged until day 180. A monolayer of factor VIII-positive cells also appeared at the neck orifice on day 14 and covered the entire orifice until day 180. The CPBs were stably localized in the sac without degradation or signs of inflammation. CONCLUSIONS CPBs may be promising as embolic materials that can induce stable vessel wall regeneration at the neck orifice of an aneurysm without surrounding inflammatory reactions.