An outbreak of coli-septicemia with a high morbidity rate of 60% and mortality of about 10% in 14-week-old peking ducks at Assiut Governorate was recorded during 1990. Bacteriological examinations of slaughtered and sick birds revealed the isolation of pathogenic E.coli serotype 073:K80. Experimental infection proved that the isolate was pathogenic to 12-weeks duck by parenteral injection and intratracheal administration. In vitro sensitivity test revealed that the isolate was sensitive to tetra cycline, chlortetracycline, furazolidone and chloramhenicol. According to the previous results chlortetracycline in water at a rate of 24 mg/bird for 5 successive days was used for controlling the infect ion.