Billy Amstell (20 August 1911 – 19 December 2005) was a British jazz reedist.
Amstell first played piano at age ten, then learned to play alto sax by himself at age 13. He played locally in Glasgow before moving to London in 1930, where he played with Jack Harris, Roy Fox, and Spike Hughes (1931). In 1932 he joined Bert Ambrose's band, where he played primarily tenor saxophone and worked well into the 1940s. He worked with Geraldo in the late 1940s and played with the BBC Dance Orchestra for five years in the 1950s. The 1960s saw Amstell do an increasing amount of studio work, including with George Chisholm; by the 1980s he was recording more often on clarinet, and released an album under his own name, Session After Midnight, in 1980. He wrote an autobiography in 1986, Don't Fuss, Mr. Ambrose, and continued to perform occasionally into his nineties.
Amstell's brother Mickey Amstell also played saxophone.