Psy・S [sáiz] (サイズ) (often written as "Psy-S" or "Psy S" in English due to the lack of the Japanese dot "・" on most Western keyboards) was a Japanese progressive pop/rock band, formed in 1983 by Masaya Matsuura alongside female vocal powerhouse Chaka (a pseudonym used by Mami Yasunori). After Japanese hits and successes throughout the late 1980s and early 1990s, they disbanded in 1996.

Their musical style was an experimental mixture of electronic synthesizers, highly accomplished electric guitar riffs, and haunting, piercing vocals.

They were also known in Western regions for the opening theme and the soundtrack on the OVA adaption of To-Y from manga artist Atsushi Kamijo. Frontman Masaya Matsuura went on to provide several video games for PlayStation.