China Eastern Airlines said in a statement to the Hong Kong stock exchange that the lion's share of the orders, nearly USD 6 billion, will go to Airbus for 20 A350 aircraft.
It will also spend close to USD 4 billion on 15 Boeing 787-9 Dreamliners.
The bitter aerospace rivals have been in a fierce battle for orders in China, which is forecast to have 1.7 billion air passengers by 2034, and is poised to become the largest civil aviation market in the world in the next two decades.
The Shanghai-headquartered company plans to use the long-haul planes for travelling between China, North America and Europe, and to replace retired aircraft.
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They were intended to build "a streamlined and efficient, well-constructed and industry-leading passenger aircraft fleet", it said, and "provide vast amount of passengers with more comfortable on-board services".
China is now Airbus' largest market, accounting for nearly a quarter of the planes it delivered in 2015.
In March, the company started construction on a new USD 150 million facility in the port city of Tianjin, northern China, to deliver wide-body planes in the country.
Boeing also plans to open a completion centre in China, it announced last year. The company sold 300 aircraft worth a record $38 billion during President Xi Jinping's visit to the US in 2015.
The China Eastern orders come a day after Boeing reported an 8.8 per cent drop in first-quarter earnings to $1.2 billion, partly due to sluggish aircraft deliveries into a slowing global economy.
But China hopes some of the massive civil aircraft market will go to its homegrown planes.
In the long term COMAC aims to produce an even larger wide-body jet in cooperation with Russia's United Aircraft Corp, whose products include the Sukhoi Superjet 100.
China Eastern's announcement late Thursday came alongside its first-quarter results, in which it said net profits rose 66.4 per cent year-on-year to 2.6 billion yuan ($400 million).