Gorilla badly injured a 46-year-old pet keeper in Spain at the Madrid Zoo on Sunday.
The woman had both arms broken, and she also suffered injuries to her chest and head, the zoo's statement said.
According to the zoo, the woman's condition was stable but serious.
A 29-year-old male gorilla, Malabo, was able to attack a woman while she was cleaning up and distributing breakfast food.
According to the zoo, it is still unclear how the animal attacked the woman, as it had to be in another space with three doors in between.
Malabo, who has been at the zoo all his life, is said to be normally very calm.