Genetic properties and host ranges of R factors derived from Bordetella bronchiseptica of pig origin were examined. All of 61 R factors tested could confer resistance to streptomycin, sulfonamide, and aminobenzyl penicillin on their host bacteria. All of them were identified as fi− (no fertility inhibition) type and were found to exhibit no restriction of phages λ, φ80, P1, P2, T1, T3, T6, T7, W31, and BF-23. They could confer macarbomysin susceptibility on their host cells when infected. An Rte16, a representative R factor, was incompatible with both RP4 and R40a, which are classified as compatibility groups P and C, respectively. An Rte16 was conjugally transmissible to B. bronchiseptica, Escherichia coli, Citrobacter freundii, Salmonella typhimurium, and Yersinia enterocolitica, but not to Shigella flexneri, S. sonnei, Proteus mirabilis, P. vulgaris, P. rettgeri, Klebsiella pneumoniae, and Pseudomonas aeruginosa.