An adult male grey heron, Ardea cinerea (Aves: Ciconiiformes), was rescued in Mikunigaoka 590-0021, Sakai, Osaka, Japan, and euthanized because of severe injury to both legs. At necropsy, a large number of deutonymphs (hypopi) of the hypoderatid mite, Hypodectes propus (Acarina: Hypoderatidae), were found in the subcutis and in the fasciae of the adipose tissue in the pectoral muscle and abdominal regions. The mites were 1.26 mm in length and 0.35 mm in width on average. The present hypopi were identified as H. propus, based on the dimensions of the mite, together with the distinct typical coxal apodemes in the anterior part. The present case reported the subcutaneous mite, H. propus, in the grey heron, A. cinerea, as a new host record in Japan.