The mine's December quarterly run-of-mine production came to 1.3 million tonnes, which is 33% greater than the previous corresponding period.
Production rates at the end of the year also increased Middlemount's annual output compared to 2019.
The mine's 2020 RoM production of 4Mt was 18% higher than the 2019 figure of 3.4Mt.
"The mine continues to focus on managing costs and improving mine operating efficiencies," Yancoal said.