The population of a lycaenid, Shijimiaeoides divinus asonis (Matsumura) has been reduced by environmental changes in some habitats in the Aso area. We conducted route census surveys of this butterfly in 2006 and 2007. The study area is located on the volcanic slopes of Mt Aso in the center of Kyushu, Japan. At the study site, the natural herbaceous grassland, which had been almost completely grazed, was subjected to routine grassland burning every spring. The results obtained are summarized as follows: (1) Pleioblastus chino (Franch. et Savat.) Makino var. viridis (Makino) S. Suzuki was one of the dominant species at the study sites with normal grazing intensity. Zoysia japonica Steud. was one of the dominant species with high grazing intensity. On the other hand, Miscanthus sinensis Anderss. was the dominant species at non-grazing sites. (2) The individual density of the host plant, Sophora flavescens Ait. was significantly different at each study site. (3) The height of the host plant at the non-grazing sites was higher than at other study sites. (4) The number of branches of the host plant at the sites with normal grazing intensity was larger than at other sites. (5) The individual crown area was bigger at the sites with normal grazing. On the other hand, the height and crown area of the host plant at sites with high grazing intensity was smaller than at sites with other grazing intensities. (6) Adult butterflies appear in early May almost disappear by mid June. Individual numbers were affected by low temperatures from April to May, and the density of butterflies markedly decreased in 2007 at all study sites. (7) The number of larvae was significantly different at each study site when population density became high. (8) The number of adults and eggs increased alongside an increase in the number of nectar plants at the grassland where grazing ceased. Based on these results, it is concluded that customary grazing intensity is most suitable for the conservation of this butterfly in the Aso area.