The fire started on the top floor of the university’s five-storey Fry Building, which was unoccupied as it was undergoing a major refurbishment worth £33m.
Seven fire engines were sent to the scene and the blaze was extinguished shortly before 8pm on Saturday.
No injuries were reported and Avon Fire and Rescue Service said everyone was accounted for.
“A fire broke out in our Fry Building at just after 5pm this evening,” a university spokesperson said.
“The building is currently undergoing refurbishment and was due to reopen in summer 2018.”
They added: “We will be working with Avon Fire and Rescue in the coming days to help investigate the cause of the blaze.”
The fire did not appear to have spread to other floors or surrounding buildings, which were also unoccupied.
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Images posted to social media showed large flames and smoke billowing from the scene, close to the city’s Wills Memorial Building.
Bristol University said the Wills Memorial library would be closed on Sunday but they expect business as usual on Monday.