Miecław (also Masław, Mojsław and Miesław, ?-1047), in the Latin of chronicler Gallus Anonymus Meczzlavus, was a pincera (cup-bearer) of Duke Mieszko II of Poland, and a rebel who tried to detach himself and Masovia from the Polish state by creating his own country
Little is known about his early life. Initially he was a cup-bearer of Mieszko II and the governor of Masovia. However, an internal crisis and a pagan reaction led to the exile of Mieszko and rule of Bezprym. This weakened the Piast overlordship over Masovia. Initially, Mieszko's successor, Casimir I, did not have enough power to reunite the country and the region succumbed into chaos. The pagan reaction in Masovia was particularly strong and it is assumed that Miecław, having achieved delegated authority in Masovia under Mieszko, simply took advantage of the difficult situation to increase his rights or become independent.
However, Casimir I in 1039 was supported by Henry III, Holy Roman Emperor against the Bohemians and soon afterwards he also concluded an alliance with Kievan Rus. This allowed him to gather enough forces to subdue Miecław. In 1047 he was attacked by the joint forces of Casimir I and Yaroslav I the Wise and was probably killed in a battle on the banks of Vistula.