The pieces of bark were found at an excavation site near the Novgorod Kremlin's fortress wall on Wednesday and Thursday.
Experts said they dated back to the first part of the 12th century, based on the occupation layer and other signs.
Archaeologists did not disclose the texts. They only said one of the findings was a note written by a woman to her acquaintance in which she reprimanded the latter for not paying her debt. The other piece is said to be part of a larger document not found so far.
A total of 956 pieces of birch bark have been found near Veliky Novgorod in the past 54 years.
Scientists found three ancient documents during this excavation season.
The first bark document did not contain profanities, but was rather unusual. It said a Velikiy Novgorod resident, known as Shilnik, had stolen pigs and horses.
The Novgorod State Museum said the first ancient document containing indecent words had been found in the town of Staraya Russa, near Novgorod.
In it, a man was advising his brother on how to trade, recommending he remain silent and do as instructed.
Historians said half-jokingly if the author had known his letter would be found nearly a thousand years later, he would have signed it and thereby gone down in Russian history as the first foul mouth.
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The Brest-Litovsk peace treaty that ended Russia’s part in the war has been the subject of heated debate from the moment it was signed in March 1918. To this day, scholars offer differing interpretations of the circumstances that led to the treaty and its domestic and foreign policy importance.