The value of the deal is $6.3 billion, based on list price, chairman Trinh Van Quyet told Bloomberg. With the previous order of 24 aircraft of the same model last year, the airline has ordered 50 in total.
Quyet said that the first of the A321Neo planes will be delivered in 2022.
Bamboo Airways had previously said that it was considering purchasing 25 narrow-body Boeing 737 MAX, which has been grounded internationally after two deadly crashes within a space of five months.
Last month, Bamboo Airways had inked a deal with Boeing for 10 wide-body 787-9 Dreamliners worth almost $3 billion.
Starting this year, the airline operates 17 domestic flight routes. It plans to start international flights next month, with Japan, Singapore and South Korea mentioned as possible destinations.
It also plans to fly to Europe in June and directly to the U.S. by the end of this year or early next year.
Bamboo Airways is one of five airlines operating in Vietnam. The others are state-owned Vietnam Airlines, budget airline Vietjet, low-cost carrier Jetstar Pacific and Vietnam Air Services Company (VASCO).
Local airlines served almost 50 million passengers last year, up 10 percent from 2017.