Octavian Nemescu (29 March 1940 – 6 November 2020) was a Romanian composer of orchestral, chamber, choral, electroacoustic, multimedia, metamusic, imaginary and ritual works.

Born in Pașcani, Nemescu studied from 1956 to 1963 at the National University of Music in Bucharest, where he took composition with Mihail Jora, harmony with Paul Constantinescu and orchestration with Alexandru Pașcanu and Anatol Vieru. In 1972 he participated in the Darmstadt summer courses. From 1971 to 1978 he taught music analysis and counterpoint at the Transilvania University of Brașov. Until 1990 he was professor of counterpoint, harmony and music history at the George Enescu National University of Arts in Iași. Since then he was a professor of composition at the National University of Music in Bucharest.

Nemescu died in Bucharest at age 80. He was the father of the Romanian film director Cristian Nemescu (1979–2006).