Nil by Mouth may refer to:

• Nothing by mouth or nil by mouth, a medical instruction
• Nil by Mouth (album), a 2015 album by Blancmange
• Nil by Mouth (charity), an anti-sectarian charity in Glasgow, Scotland
• Nil by Mouth (film), a 1997 British film directed by Gary Oldman
• "Nil by Mouth", a 2001 song by Blindspott
• "Nil by Mouth", a 2018 instrumental by Haken from Vector
• "Nil by Mouth", a 2021 song by Dean Blunt from Black Metal 2