Nikolai Girshevich Kapustin (Russian: Никола́й Ги́ршевич Капу́стин; born November 22, 1937 in Horlivka, Ukrainian SSR) is a Russian composer and pianist.

Kapustin studied piano with Avrelian Rubakh (pupil of Felix Blumenfeld who also taught Simon Barere and Vladimir Horowitz) and subsequently with Alexander Goldenweiser at the Moscow Conservatory. During the 1950s he acquired a reputation as a jazz pianist, arranger and composer. He is steeped, therefore, in both the traditions of classical virtuoso pianism and improvisational jazz.

He fuses these influences in his compositions, using jazz idioms in formal classical structures. An example of this is his Suite in the Old Style, Op. 28, written in 1977, which inhabits the sound world of jazz improvisation but is modelled on baroque suites such as the keyboard partitas composed by J. S. Bach, each movement being a stylised dance or a pair of dances in strict binary form. Other examples of this fusion are his set of 24 Preludes and Fugues, Op. 82, written in 1997, and the Op. 100 Sonatina.

Kapustin regards himself as a composer rather than a jazz musician. He has said, "I was never a jazz musician. I never tried to be a real jazz pianist, but I had to do it because of the composing. I'm not interested in improvisation – and what is a jazz musician without improvisation? All my improvisation is written, of course, and they became much better; it improved them."[1]

Among his works are 20 piano sonatas, six piano concerti, other instrumental concerti, sets of piano variations, études and concert studies.

Russian and Japanese record labels have released several recordings of the composer playing his own music. He has also been championed by a number of prominent pianists, including Steven Osborne, Marc-André Hamelin, Ludmil Angelov and Japanese pianist Masahiro Kawakami, who released CDs devoted to Kapustin.

Theoretical physicist Anton Kapustin is his son.