Iris rossii Baker (Iridaceae) is one of the threatened plants growing in secondary grassland with sparse pine forest. The aim of this research is to investigate current status in a protected area for I. rossii population, and obtain knowledge for conservation of the population. The flora of vascular plants and vegetation were investigated in the protected area for I. rossii in Hofu City, Yamaguchi Prefecture. Investigations were mainly carried out in June and November 1990 at the three different habitats. As a result, a total of 153 species of 62 families were recorded in whole area. Only Erigeron sumatrensis was recorded as a naturalized plant species in the protected area in 1990. Species composition of the closed forest area, where no I. rossii were found, was different from those of the sparse forest area and the grassland area. Therophytes and hemicryptophytes were seen mainly in the grassland area. Nanophanerophytes, microphanerophytes, mega- and mesophanerophytes and lianas were mainly in the closed forest area. Two vulnerable species, I. rossii and Calanthe discolor listed in the Red Data Book and seven designated species including I. rossii listed in the national and quasi-national parks in Japan were found to have grown mainly in the grassland area and the sparse forest area.