Separately, Boeing and Bombardier said the airline had also ordered aircraft from them.
Bombardier, meanwhile, said Ethiopian had signed a purchase agreement for an additional five of its Q400 turboprop aircraft.
Ethiopian wants to increase revenue to $10 billion by 2025 and expand its fleet to 140 aircraft from less than 90 now, with sights set on Asia.
Ethiopian Airlines has placed an order for 10 Airbus A350-900 passenger jets, it said on Tuesday, in addition to at least another 10 it already has on order.
Separately, Boeing and Bombardier said the airline had also ordered aircraft from them.
The A350-900s will be deployed on Ethiopian's long haul routes connecting Addis Ababa with destinations in Africa, Europe, the Middle East and Asia, Chief Executive Tewolde GebreMariam said in a statement.
The state-owned carrier is ranked the largest in Africa by revenue and profit by the International Air Transport Association (IATA), the global industry body.
Boeing said Ethiopian had signed a commitment to buy two 777 freighters in an order valued at $651.4 million at list prices.
It added the airline had also ordered another 10 737 MAX 8 planes, exercising options from a 2014 order, bringing Ethiopian's total orders for 737 MAX 8s to 30.
Bombardier, meanwhile, said Ethiopian had signed a purchase agreement for an additional five of its Q400 turboprop aircraft.
In February, Tewolde told Reuters that Ethiopian's revenue rose 10.3 per cent to 54.5 billion birr ($2.43 billion) in the 2015/16 fiscal year, while passenger numbers climbed 18 per cent to 7.6 million.
Net profit was up 70 percent at 6 billion birr.
Ethiopian wants to increase revenue to $10 billion by 2025 and expand its fleet to 140 aircraft from less than 90 now, with sights set on Asia.
