The pharyngeal villiform processes of the hibernating soft-shelled turtle, Trionyx sinensis japonicus, were studied by immunohistochemistry for Na+/K+-ATPase in combination with a mitochondrion staining. Mitochondria-rich cells were recognized in the epithelium constituting the distal part of most processes, and exclusively showed the Na+/K+-ATPase immunoreactivity. These cells tended to attract each other to form clusters. When considering the physiological and histological data previously obtained in corresponding cells in the fish gill epithelium, the mitochondria-rich cells in the hibernating turtle were suggested to be involved in the electrolyte (Na+) uptake from the aquatic habitat.