The undo mechanism is an essential feature in collaborative editing systems. Most popular semantic wikis support a revert feature, some provide an undo feature to remove any modification at any time. However this undo feature does not always succeed. Supporting the undo mechanism for P2P semantic wikis has never been tackled. In this paper, we present an undo approach for Swooki the first P2P semantic wiki. We identify the problems to resolve in order to achieve such mechanism for P2P semantic wikis. We give the definition of the undo and the properties that must ensure. This approach allows both a revert and a permanent successful undo.