ALEXANDRA OLGERDOVNA (c. 1360 in Vilna - † April 20 / June 19, 1434 in Plotsk), Princess of Lithuania, since 1387 the wife of Siemowit IV, Prince of Mazovia, sister ofVladislaus II Jagiellon (of Hungary), the Grand Duke of Lithuania and King of Poland

• Algirdas Gediminovich, the Grand Duke of Lithuania (1345-1377)

• Juliania Alexandrovna of Tver, the second wife of Algirdas, daughter ofAlexander Mikhailovich, the Grand Prince of Tver and Anastasia

The daughter of the Grand Duke of Lithuania Algirdas and Juliana of Tver, Alexandra was born in the late 1360s. [2, p. 306]. Since the exact date of her birth is unknown, it is impossible to reliably determine the seniority of the princess among her brothers and sisters.

In 1387 her elder brother Jagailo, who had been crowned a year before as Vladislaus II, gave Alexandra to the Masovian prince Siemovit IV as a wife [4, p. 64-66]. In the face of a constant struggle for power, Alexandra's marriage removed one problem from Jagiello-Vladislaus: Siemovit, as a representative of the Piast House, could lay claim to the Polish throne [1, p. 57-82]. In exchange for the principality of Belsk and 10,000 grosz paid as a dowry, Siemovit renounced his claims to the Polish throne [5, p. 7; 6, s. 76-81].

In marriage Alexandra had 12 (according to other sources - 13) children [2, p. 306; 3, p. 904; 4, p. 64-66].

Alexandra died on April 20 / June 19, 1434 in Plock. She was buried in the Plock Cathedral.  

• Siemowit V of Rawa, Prince of Plock (1426–1434), Belz (1426–1434), Wizna (1426–1434 гг.) and Rawa (1426–1442 гг.)
• Casimir II of Belz, Prince of Plock (1426–1434), Belz (1426–1442), Rawa (1426–1434) and Wizna (1426–1434)
• Wladyslaw I of Plock, Prince of Plock (1426–1455), Wizna (1426–1455), Belz (1426–1434, 1442–1455) and Rawa (1426–1434, 1442–1455)
• Trojden II, Prince of Belz (1426–1427), Wizna (1426–1427) and Rawa (1426–1427)
• Alexander of Masovia, Bishop of Trento
• Cymburgis of Masovia, the wife of Ernest I, Duke of Austria(1377–1424)
• Euphemia of Masovia, the wife of Bolesław I, Duke of Bytum, Cieszyn, Toszek (c. 1363–1431)
• Hedwig of Masovia, the wife of Janos Garai(† 1428)
• Amelia of Masovia, the wife of William II, Margrave of Meissen co-ruler of Saxony (1371–1425)
• Anna of Masovia, the first wife of Michael Žygimantaitis of Lithuania, son of Sigismund Kęstutaitis, the Grand Duke of Lithuania
• Maria of Masovia, Duchess of Pomerania, the wife of Bogislaw IX, Duke of Pomerania (c. 1407/1410 – 1446)
• Catherine of Masovia, the third wife of Michael Žygimantaitis, Prince of Lithuania, son of Sigismund Kęstutaitis, the Grand Duke of Lithuania

Benon D. Walka Siemowita IV o koronę polską // Rocznik Mazowiecki. T. 11. 1999. S. 57–82.

Gudavičius E.Aleksandra // Antanas Račis (ed.). Visuotinė lietuvių enciklopedija. Vilnius, 2001. 

Jasiński K. Rodowód Piastów mazowieckich. Poznań–Wrocław, 1998.

Piotrowicz K.Aleksandra // Polski Słownik Biograficzny. T. 1. Kraków, 1935. P. 66–67.

Stone D. The Polish–Lithuanian State, 1386–1795. A History of East Central Europe. University of Washington Press, 2001.

Supruniuk A. Siemowit IV // Polski Słownik Biograficzny. T. XXXVII/1, zeszyt 152. Warszawa–Kraków, 1996. S. 76–81.