This small piece is now well known as "Nocturne", however, there is no description of "Nocturne" on his original score. It was written for Ludwika (his elder sister)’s etude for playing concerto No.2 Op.21, in 1830 when he was 20 years old. It was substantially an improvisation, but full of melancholic beauty. This piece has a short intermediate part supposed to be unfinished. The part has a structure of [A-B-C-B]-[A-B-C-B]-[C-B]-C in which each A/B/C corresponds to a bar. In this arrangement, this part was condensed to [A-B-C-B]-C to avoid redundant impression.　The other part is faithful to the original notes.