Autoradiography was used to visualise an internal radiation in the vibrissae of a wild masked palm civet (Paguma larvata) carcass found in a highly radioactive contamination area within 50 km from the Fukushima Dai-ichi Nuclear Power Plant accident site. Autoradiogram of the vibrissae revealed a higher density in the root than in the shaft showing a stripe pattern; the γ-ray spectrum of the vibrissae showed peaks of 134Cs and 137Cs. The radiocaesium taken into the body was responsible for its distribution into the vibrissae shaft during its growth. The stripe pattern indicated that internal radiation exposure was intermittent. This finding suggests that autoradiography of vibrissae is a suitable method for assessment of the history of internal radiation exposure in wild mammals, such as masked palm civet.