GT3 may refer to:
Automotive 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 Group GT3, a class of auto racing FIA GT3 European Championship, a defunct series based on Group GT3 GT3 (1998–1999), a former class of auto racing for grand touring cars, used by IMSA and the SCCA
Other uses Gran Turismo 3: A-Spec, a 2001 car racing game developed for the PlayStation 2 British Rail GT3, a prototype gas turbine locomotive Denel GT-3, a South African 105mm cannon