Trichophyton mentagrophytes were isolated from 19 of 20 guinea pigs in a children’s corner of a zoo. The nucleotide sequence identity of the internal transcribed spacer region among 19 guinea pig isolates was 99%, including the reference strain of animal type 3 of T. mentagrophytes. The genomic DNA of all isolates were investigated for the mating (MAT) gene by specific polymerase chain reaction. The alpha-box gene was detected in all 19 isolates, while the high-mobility-group (HMG) gene was detected in only one of 19 isolates. Therefore, the guinea pig population harbored at least 2 MAT types of Arthroderma vanbreuseghemii. The T. mentagrophytes that was prevalent in this population may constitute a constant source of infection for persons coming into contact with guinea pigs.