Simon Hugh "Si" Zentner (June 13, 1917 in New York City – January 31, 2000 in Las Vegas, Nevada) was an American trombonist and jazz big-band leader.

Zentner played violin from age four and picked up trombone a few years later. As a teenager, he was awarded the Guggenheim Foundation Philharmonic Scholarship. He attended college for music and had intended to pursue a career in classical music, but became more interested in pop music after recording with Andre Kostelanetz. Zentner played in the bands of Les Brown, Harry James, and Jimmy Dorsey in the 1940s, then moved to Los Angeles, where he worked as a studio musician. He also landed a job with MGM from 1949 to the mid-50s, and was involved in the music for films such as Singin' in the Rain and A Star Is Born.