Despite the fact that the Second String Quartet by Borodin is well-known, there are some unsolved problems relating to it. The manuscript sources from the National Library of Russia and St. Petersburg State Conservatory are thoroughly examined in the given article. The analysis of all the sources makes clear the main stages of Borodin’s work on the Second Quartet, the sequence of composition of each movement, and some features of the composer’s methods of work. Only two life-time performances were previously mentioned by scholars. The date of the third life-time performance of the Second Quartet is now established; and the only life-time review is entered into scientific use. The discrepancies between the full autograph score and the first (posthumous) edition are defined and systemized. So the problem should be raised, whether the above-mentioned edition corresponds to author’s intentions.