A spokesperson for the Emirates airline said in a statement on Tuesday: "Emirates confirms it will not be taking delivery of its order and options for 20 Airbus A340-600 aircraft."
Emirates officials have previously indicated that they were not happy with the aircraft's efficiency and could cancel further orders.
The news comes after the airline's latest threat to "exercise all options" on the delay in the delivery of 45 A380 superjumbos, now scheduled to start in August 2008, instead of October 2006, 22 months later than scheduled.
Emirates is also looking to lease seven Boeing 777s to bridge the gap in demand and capacity.
Although Emirates did not give any precise reason as to why it is switching away from Airbus, analysts believe delays in production coupled with the better performance of Boeing's twin-engined 777 series could be the reason.
The Arab airline operates a fleet of 99 aircraft, 48 of which are made by Airbus.
The airliner placed orders for 71 aircraft in 2003 worth $19 billion, including 45 A380s and 26 B777s, followed by another order involving 42 Boeing 777s worth $9.5 billion at list price.
The airline is sending a team of engineers to Toulouse to review the performance of the superjumbo and the accuracy of the new delivery dates.
The airline is keen to see that Airbus maintains the latest schedule, the spokesperson said.