Flag of Ainz Ooal Gown is the flag that represented the guild of Ainz Ooal Down in YGGDRASIL.
The flag banner is located on the 10th Floor of the Great Tomb of Nazarick. It can be seen hanging behind the throne. During his stay in the New World, the Overlord points toward this flag, declaring to Nazarick's NPCs that he will no longer be called "Momonga" but now "Ainz Ooal Gown." 
The Flag of Ainz Ooal Gown is also being used as a national flag to its home country, the Sorcerer Kingdom for political purposes. For instance, it was shown during a meeting between the Roble Holy Kingdom and the Sorcerer Kingdom that takes place at E-Rantel.
Albedo was hateful and hostile to this flag as it reminded her of the fact that almost all the Supreme Beings except Momonga have abandoned Nazarick's NPCs. It came to a point where she left the Flag of Ainz Ooal Gown crumpled on the floor in her secret space. At the same time, she went as far as to trample the flag with her foot without showing any hint of respect towards it.
The flag banner is embroidered with the symbol of Ainz Ooal Gown.
Despite there having not been any indication of its abilities being known, this flag serves to represent Ainz Ooal Gown as a guild. Such a sigil-like symbol imprinted on the flag stands for every guild member who happens to be part of the same association.
- Season 1 Opening of Overlord (Anime), shows Ainz taking away the Flag of Ainz Ooal Gown from Albedo and then holding it up high with Nazarick's NPCs standing beside him right before the song Clattanoia ends.
- Although for different reasons, both Albedo and Philip were the only two known individuals out there so far to have trampled the flag on the ground and dirty it.