MGS may refer to:
- MgS, the molecular formula for magnesium sulfide
In multimedia:
- Metal Gear Solid, a 1998 stealth action video game
In schools:
- Manchester Grammar School, England
- Maidstone Grammar School, Kent, England
- Melbourne Grammar School, Australia
- Methodist Girls' School, Singapore
- Middleton Grange School, New Zealand
In mathematics:
- Modified Gram-Schmidt, a method of orthogonalizing a set of vectors
In other uses:
- Multiple gunshot suicide
- Mars Global Surveyor, an American spacecraft launched in 1996
- Modelling of General Systems, a domain-specific language for biological systems
- Stryker Mobile Gun System, an armored fighting vehicle
- Mason Gray Strange, Auctioneers & Valuers of Plant & Equipment Australia Wide