Fusobacterium Nucleatum is an anaerobic commensal microorganism present in the oral cavity and some mucous membranes with great capacity to form biofilm. In the literature, only one case of acute periprosthetic infection of the knee by Fusobacterium Nucleatum has been reported, providing the second case. A 72-year-old man presented with an acute periprosthetic infection by fusobacterium nucleatum after a second time of a prosthetic knee replacement. Debridement and spacer changes were performed up to 4 times, associating parenteral antibiotic treatment. After ensuring the absence of infection, a modular revision knee prosthesis with stems was placed, with a satisfactory evolution after two years. Currently he has preserved ambulation, joint balance of 0º-50º and is free of infection. Fusobacterium Nucleatum infection is very rare, but aggressive and difficult to resolve, recommending two-stage replacement in acute infection and adequate antibiotic treatment to offer curative treatment.