Solidago altissima L. is a perennial naturalized plant belonging to Compositae and originated in the temperate eastern North America. Its rhizomes run under-ground and its stem stands straight and grows more than 2m. They have strong vegetative reproductive ability and grow densely in various habitats. They are widely distributed and are now subjected for removal. Generally, it is said that mowing is the most effective way of removal because it is safe and cost effective. The purpose of this study is to understand the influence of mowing on their growth. The study was conducted in Higashi-Hiroshima City, western Japan. Three quadrats (1m×1m) were established in open lands near Hiroshima University. One quadrat was established in a homogenous community with no mowing for the last few years. The remaining two were established in a homogenous community, as well, but with mowing. The former plot is called control plot here and the latter two are called mowing plots. Stem was defined as ramet of the above ground in this study. The numbers, the height and the thickness of ramets in control plot and mowing plots were measured in February 1999. The size of shoots and shoots from original mowed stems in one mowing plot were also investigated in October 1999. As the results, the number of ramets was larger, and the height and thickness of ramets were lower in the mowing plots than the control plot. The thickness of shoots was about half of the original stems. The reactions of this species to mowing might be the result of their priority over producing seeds than their growth. Inherently this species do not have any nature to regenerate by shoots. However it seems they indicate this nature as a reaction to mowing.