The aim of this study was to investigate Proteus vulgaris infections in sharptooth catfish, Clarias gariepinus, in Assiut, Egypt. Clinical and findings of infected fish and seasonal prevalence of postmortem infection were investigated. Pathogenicity of Proteus vulgaris was also assessed. Out of 120 fish showing skin lesions and signs of septicemia examined over year 2005, only 1.58 %) fish were infected with Proteus 36 Assiut Vet. Med. J. Vol. 52 No. 111 October 2006 vulgaris. Bacteria identification was based on colony morphology and culture behavior on various media, microscopic examination, biochemical tests and carbohydrate fermentation. Strain K93PV isolated from kidneys of infected fish was used throughout this study. Seasonal prevalence of Proteus vulgaris infections increased over spring and reached maximum in summer. Infection was not recorded in winter. Lethal dose 50 (LD50) of Proteus vulgaris in sharptooth catfish was 1.25X10'cfu/100g fish body weight intramuscularly injected. Clinical and postmortem examination of experimentally infected fish revealed that skin lesions and sometimes generalized septicemia are the predominant signs associated with Proteus vulgaris infection.