The study was carried on 100 Procambarus Clarkii collected from the small tributaries of El-Ibrahemia canal, Assiut city. The clinical signs and postmortem lesions of red swamp crayfish were recorded. P. clarkii were subjected to bacteriological examinations. The isolated bacteria were identified as Streptococcus faecium. The percentage of infection was 36 % among the examined crayfish. Isolates were isolated from haemolymph, hepatopancrease and brain. Experimental infection was successful through intraperitoneal injection of Nile tilapia. The clinical signs were darkening in colour, haemoragic skin and fin. The fish showed gasping air, detachment of scales and skin erosion and ulcer. The common postmortem lesions were congestion of internal organs. The aforementioned bacterial isolate was successfully re-isolated from experimentally infected fish