B minor or B-flat minor is a minor scale based on B-flat. Its key signature has five flats.

Its relative major is D-flat major, and its parallel major is B-flat major. Its enharmonic equivalent is A-sharp minor.

B-flat minor is often seen as a "dark" key." Tchaikovsky said that the oboe solo in B-flat minor in the second movement of his Symphony No. 4 was "the feeling that you get when you are all alone".

The old valveless horn could not play easily in B-flat minor. In fact, the only example found in 18th century music is a modulation in the first minuet of Franz Krommer's Concertino in D major, Opus 80.