A group of animal rights campaigners from the organisation Direct Action Everywhere (DxE), arrived at the fast food restaurant in London Road.
Activists sprayed blood on the floor while and held up posters.
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"It violence, it's not food!" the activists chanted.
"Fake blood I spilt is nothing compared to the real blood McDonald's has spilled," said one of the campaigners.
Sussex Police officers arrived at the scene and urged the activists to leave, making one arrest, according to the group's Facebook page.