A novel bacteriophage, φMR25, was isolated from a lysogenic Staphylococcus aureus strain by mitomycin C induction. Its biological features were analyzed in comparison with φMR11, which was described previously as a prototype therapeutic phage. φMR25 is morphologically similar to φMR11 (morphotype B1 of family Myoviridae) but has a broader host range than φMR11 on S. aureus strains. φMR25 can also multiply on S. aureus lysogens of φMR11. Its DNA is 44,342 bp in size, is predicted to include 70 open reading frames, and does not contain genes related to toxin or drug resistance. The lysogenic module and most of the putative virion protein genes are completely different from those of φMR11. In spite of their genetic diversity, intraperitoneal administration of φMR25 rescued mice inoculated with a lethal dose of S. aureus, as was the case for φMR11. These results suggest that φMR25 could be another candidate phage to treat S. aureus infection. © Springer-Verlag 2010.