The prevalence of hemotropic mycoplasmas in wild rodents is largely unknown. Here, we report the presence of hemoplasmas in blood samples collected from brown sewer rats (Rattus norvegicus) trapped during rodent control around an animal hospital in Morioka, Japan. We examined nine rats using real-time PCR and end-point PCR, and found one rat (11.1%) that was positive for a hemoplasma infection. The 16S rRNA gene and 16S to 23S rRNA intergenic spacer region of the hemoplasma detected in a wild-caught rat were amplified using PCR. The nucleotide sequences of the PCR products were further determined and compared to those of other hemoplasmas. Our examinations revealed the presence of a hemoplasma that has not previously been described in rodents. The pathogenic traits of this hemoplasma remain unexplored.