The Japanese Marsh Warbler Megalurus pryeri is an endangered grassland passerine species and their distribution is restricted to a few marsh lands in Japan. To collect information important to conservation of the species, habitat characteristics of male warblers in the breeding season was studied at Hotoke-numa reclaimed area, northern Honshu, Japan, in the summer of 1993. Vegetation structure was significantly different between areas available and unavailable for male warblers. Specifically, the density of sedges (Carex spp.) was higher, and the density of reeds (Phragmites communis) was lower, in available area. These results suggested that sedges may play an important role in breeding activities of Japanese Marsh Warblers and maintenance of such vegetation can be important for conservation of the species.