Hortaea werneckii, a black yeast and the causative agent of tinea nigra (a superficial type of dermatomycosis), is a human pathogen and is also found in the environment. It is not highly pathogenic but in the last fifteen to twenty years has been isolated from various human and environmental sources in Japan. As far as we know, there has been no report on the isolation of H. werneckii from animals. Recently, we found a case of a guinea pig with dark superficial lesions on the palm and dorsal areas. Cultural and morphological studies of scrapings from the lesion showed that the causative agent was a black yeast, which was identified as H. werneckii by morphological study and molecular biological screening. D1/D2 region of the 26S large subunit rDNA gene of this isolate was identical to those of 11 other H. werneckii isolates used as reference strains in this study. This is the first case recorded of tinea nigra caused by H. werneckii in a guinea pig.