The 2011 Australian motorcycle Grand Prix was the sixteenth round of the 2011 Grand Prix motorcycle racing season. It took place on the weekend of 14–16 October 2011 at the Phillip Island Grand Prix Circuit.

The 2011 Grand Prix motorcycle racing season was the 63rd F.I.M. Road Racing World Championship season. The 2011 season was also the final season for 800cc engines in MotoGP, and also for 125cc machinery, as both MotoGP switched back to 1000cc engines and a new four-stroke Moto3 class was also introduced in 2012. Casey Stoner was crowned as MotoGP World Champion for the second time, following his ninth victory of the season at the Australian Grand Prix. Stoner, who was champion previously in 2007, finished 16 of the 17 races to be held in the top three placings – equalling a premier class record held by both Valentino Rossi and Jorge Lorenzo – including ten wins to become the final 800cc champion before the premier class reverted to 1000cc engines in 2012. As of 2022, this was the last time the premier class was won by a non-European rider, and also the only season in the 2010s decade that the premier class was won by a rider other than Marc Márquez or Jorge Lorenzo. The Moto2 title was decided before the final race of the season at the Valencian Grand Prix. Stefan Bradl became Germany's first motorcycle World Champion since Dirk Raudies won the 1993 125cc World Championship title after Marc Márquez, the only rider that could deny Bradl of the championship, was ruled out of the race due to injuries suffered during free practice at the Malaysian Grand Prix. The final 125cc world championship title went to Spain's Nicolás Terol, after he finished second in the final race of the season in Valencia, and his only title rival Johann Zarco crashed out during the early stages of the race. Terol, who finished third in the class in 2009 and second to Márquez in 2010, ended the season 40 points clear of Zarco, with Maverick Viñales 14 points further behind, after winning the final two races of the season. The season was marred by the death of Marco Simoncelli at the Malaysian Grand Prix.