The switch to the larger planes is an option after Qatar Airways refused to accept four A320 neos earlier this year over issues with the aircraft's engines.
"Yes, we have cancelled a few deliveries," said the airline's chief executive, Akbar Al-Baker, speaking in Doha.
"We are in negotiation with Airbus, how we can continue our relationship and keep our order on track, minus the ones that we cancelled."
Baker said Qatar Airways was "renegotiating" the contract to change the A320s to A321s and for the newly ordered aircraft to have engines from a different manufacturer.
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The engines on the cancelled planes were made by Pratt and Whitney.
Baker said that deliveries of the new planes would begin in 2018.
In October, the airline announced an order worth up to USD 6.9 billion (6.5 billion euros) with Boeing for up to 100 aeroplanes.