We isolated Streptobacillus moniliformis, the causative agent of rat-bite fever in humans, from the salivary gland of a pet rat postmortem. The isolate was a Gram-negative pleomorphic coccobacillus, which produced acid from glucose and showed enzymatic activities for eight items in the API ZYM system. The results were consistent with those of the reference strain, ATCC 14647(T), except for acid production from dextrin. Partial sequencing of 16S rRNA (1,440 bp) and gyrB genes (514 bp) of the isolate revealed similarities of 100% and 99.8%, respectively, to those of S. moniliformis in GenBank. Therefore, the isolate was identified as S. moniliformis. These results suggested the potential risk of rat-bite fever arising from pet rats in Japan.