Piotr Włostowic (c. 1080 – 1153), also known as Peter Wlast or Włost) was a Polish noble, castellan of Wrocław, and a ruler (możnowładca) of part of Silesia. From 1117 he was voivode (palatyn) of the king of Poland, Bolesław III Wrymouth. Part of the Łabędzie family, and son of Włostowic, he is likely to have been related to older princes of Silesia. His lands included the territories near Mount Ślęża and Piasek Island near Wrocław. The Dunin clan of noble families claims descent from him.
His most famous deed is the capture of Volodar (Wołodar) of Peremyshl (Przemyśl). Later he married Maria, a daughter of Sviatopolk II of Kiev. For this marriage and his adventure in Rus', he was ordered by the Church to reconcile. He was ordered to construct seventy churches.
Włostowic, a loyal subject of Bolesław III, had much more negative relations with Bolesław's son, Władysław II the Exile, and especially his wife, Agnes of Babenberg, who considered Włostowic a traitor. In 1146, Włostowic was captured by Władysław, blinded and muted. This mutilation of the popular Włostowic was one of the reasons for a civil war between Władysław and his brothers, as the blinded Włostowic went to Rus', which had so far supported Władysław, and convinced them to break their alliance. Eventually Władysław lost the war and went into exile in 1146. Włostowic regained his position and estates, but his disability and worsening health prevented him from taking further active part in politics, and he died in 1153.