Harvest mice build a nest with tall grasses, such as Common reed and Japanese pampas grass. Recently, their habitat has decreased and bank-grass mowing as river management seemed to affect on breeding of harvest mice. Grass mowing was set up in three different schedules in consideration of the harvest mouse in a bank of Kizu river; it carried out at intervals of two weeks from end of April. After the mowing, nesting distribution of harvest mouse and vegetation growth were investigated. At first, nests made of Common reed or Foxtail grass were found in the division of the mowing order, 50, 59 and 67 days after, respectively, then Common reed became main nest material. Nesting increased from May to September and breeding nests were built from July to September, a peak of breeding occurred in August. Since the average height of Common reed at the start of nesting was 120cm in all divisions, it was suggested that nesting is influenced by the height of vegetation. It turns out that the time of mowing have a great impact on the harvest mouse. Vegetation management which is necessary for a habitat of harvest mouse was discussed.