Four virulent phages-Phi D1, Phi T1, Phi CYT21, and Phi OS6, infective on Sarothamnus scoparius rhizobia-were isolated from the soil and characterized for morphology, host range, rate of adsorption to bacterial cells, and genome size. New phages were separated into two morphological families: Siphoviridae with long, noncontractile tails (Phi D1, Phi T1) and Myoviridae with long, contractile tails (Phi CYT21, Phi OS6). They were also classified into two groups by a host specificity. One of them included viruses (Phi D1 and Phi T1) that lysed S. scoparius bradyrhizobia and Bradyrhizobium sp. (Lupinus) strain D1, and the second one comprised phages (Phi CYT21 and Phi OS6) that parasitized only Scotch broom native microsymbionts. Phages specific for S. scoparius rhizobia were differentiated not only by morphology and host range but also by a genome size that was in the range from 47,583 to 60,098 b.p.