GT3
GT3 may refer to:

 Porsche 911 GT3, a high performance version of the Porsche 911
 IMSA GT3 Cup Challenge, a one-make racing series featuring the Porsche 911 GT3
 IMSA GT3 Cup Challenge Canada, the Canadian subsidiary series
 Gran Turismo 3: A-Spec, a car racing game developed for the Sony PlayStation 2. Released in 2001.
 Gemini-Titan 3 crewed spaceflight in 1965
 British Rail GT3 gas turbine locomotive
 Group GT3, a class of auto racing
 FIA GT3 European Championship, a series based on Group GT3