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Olga Konstantinovna of Russia (in Russian Великая Княжна Ольга Константиновна) (3 September 1851 - 18 June 1926), born Her Imperial Highness Grand Duchess Olga Konstantinovna of Russia, was the queen consort of King George I of Greece and in 1920, Regent of Greece.

A granddaughter of Tsar Nicholas I of Russia and cousin of Tsar Alexander III of Russia and Tsar Nicholas II, Olga was the daughter of Grand Duke Konstantin Nikolayevich of Russia and Alexandra Iosifovna, a Princess of Saxe-Altenberg. She met the young king during his trip to Russia to meet with his sister Dagmar, the Danish wife of Tsar Alexander III. They fell in love and married in 1867, when she was sixteen years old.

Together they had eight children:

Constantine (1868-1923), who succeeded his father as king.
George (1869-1957), High Commissioner of Crete.
Alexandra (1870-1891), married Grand Duke Paul Alexandrovich of Russia (son of Alexander II of Russia). Mother of Dmitri Pavlovich Romanov, assassin of Grigori Rasputin.
Nicholas (1872-1938)
Marie (1876-1940), married first Grand Duke George Mikhailovich of Russia and second Pericles Ioannides.
Olga (1881, died when three months old)
Andrew (1882-1944), father of Prince Philip, Duke of Edinburgh.
Christopher (1888-1940), father of Prince Michael of Greece.

She was acting Regent after her grandson, Alexander I died on 25 October 1920 of a monkey bite, until her son Constantine returned to take over the throne a second time. He had reigned before from 1913 to 1917 and again from 1920 to 1922.

Having been extensively involved in charity work and having endowed the Evangelismos (Annunciation) Hospital, Greece's largest, in downtown Athens, Olga was Greece's only genuinely popular Queen.