Emirates placed the order as part of a wider deal with Airbus in 2007 and had been due to receive the first extra wide body (XWB) A350 planes in 2019.
Rolls, which has major bases in Bristol and Derby, said it was hopeful that the delivery slots would be taken by other airlines but admitted that in the meantime the cancellation will reduce its order book by around 3.5%.
The loss of the Emirates order comes in a year when Rolls-Royce expects revenues and profits will fail to grow due to the impact of defence spending cuts among major customers. Shares fell 2% today.
Rolls said: "Demand for the Airbus A350 remains strong, with more than 700 aircraft and 1,400 Trent XWB engines already sold. We retain a close working relationship with Emirates and continue to support their 38 Rolls-Royce-powered wide body aircraft currently in service."
Airbus said it remains confident in its A350 programme, with 742 firm orders half a year before the plane's entry into service.
The decision to cancel the order follows the airline's commitment to buy 50 additional A380s at the last Dubai Airshow.
The planemaker said: "Airbus and Emirates benefit from a long-standing relationship and the airline recently reiterated its confidence in Airbus products particularly by praising the A380 and the benefits the aircraft brings to their operations."