"The decision... follows a number of injuries over recent years to graduates hurt by falling mortarboards," the University of East Anglia said in a statement.
"This is an unacceptable risk and we want to ensure no student's graduation day is ruined by the potential for avoidable injury," it said.
The university said that academic dress suppliers "often receive back damaged mortarboards" when students throw the hats above their heads.
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The official photographers have asked students to mime throwing their hats and have offered to add the mortarboards in digitally at no extra cost.
The graduation hat-throwing tradition started in the United States but has taken off worldwide and is often the only time that students wear academic gowns.
"If I've paid £45 to hire a bit of cloth and card for the day, I should be able to chuck my hat in the air," Louisa Baldwin, president of the university's law society, told The Tab student newspaper.
The paper said the ban was put in place after one student had to be treated in hospital last year with a serious injury after being hit by a mortarboard.
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