The singer warned one fan, saying: "It landed right by your head. Oh my God, it's a bat."
Adele was performing in Mexico City as part of her world tour, which began in Belfast in February.
After a few minutes flapping around, the bat flew away and things returned to business as usual.
It's not the first time an animal has joined her on stage - and the tour has thrown up some other surprises too.
During a concert in Los Angeles in August, Adele invited a fan onto the stage.
The man had also brought his dog along to see the British singer.
