Hygrophytic plant communities in habitats of the endangered butterfly Maculinea teleius were mowed to conserve the butterfly in Iwate Prefecture. Mowing has been undertaken in November of every year since 2006. However, despite this measure, M. teleius numbers have continued to decline in recent years. To clarify the effect of the other measure, plots adjacent to areas of M. teleius habitat were mowed in June 2011. Vegetation and environmental conditions were surveyed in the plots mowed in June (experimental) and unmowed (control) plots. Flowering shoots of Sanguisorba tenuifolia, a food plant of M. teleius, were also recorded in the experimental and control plots. The results showed that the degree of Phragmites australis dominance in experimental plots tended to be lower than in control plots. Further, the degree of S. tenuifolia dominance in both experimental and control plots decreased, although S. tenuifolia tended to be more abundant in experimental plots. However, compared to control plots, there were fewer S. tenuifolia flowers/shoot in experimental plots. Although mowing in June diminished the dominance of P. australis to some extent, mowing also reduced the number of S. tenuifolia flowers used by M. teleius for food. The structure of the plant communities in the surveyed plots will also be reported.