ThermotolerantCampylobacter strains isolated from dog feces were characterized by phenotypical tests, DNA base composition, and DNA-DNA-hybridization. Out of 98 strains, 63 were catalase negative or weakly reacting (CNW); they were found in diarrheic as well as in healthy dogs. The CNW strains were all nalidixic-acid sensitive, hippurate negative, and grew at 42°C but not at 25°C. Seven strains were further investigated. They were sensitive to 2,3,5-triphenyl-tetrazolium chloride, reduced nitrate, and produced H₂S in the lead acetate test but not in triple-sugar-iron agar. The mol% G+C for five CNW isolates ranged from 35.2–35.8, which is higher than reported for any thermotolerantCampylobacter species. The strains also formed a well-delimitated DNA homology group with 80% or more intragroup relatedness and about 40% related toC. coli andC. jejuni.