Outbreak of abortion were occurred in one of the sheep flock (175 sheep) in Tehran province, led to aborted of 8 sheep. Samples of liver, heart, abomasal contents, spleen and abdominal cavity fluid of aborted fetus were cultured in blood agar, BHI and Mc Conkey agar media. Morphological and biochemical examinations showed that casutive agent of outbreak abortion was Campylobacter fetus subsp. fetus. The bacterium was catalase and casutive H25 positive and urea ase and nitrate reduction negative.