Abstract
Recently, in Japan, high temperature is causing a decrease in rice grain weight and quality such as transparency, roundness and cracking. There is a genuine concern that ongoing global warming will seriously affect rice production. Consequently measures to prevent damage by high temperatures and knowledge on the mechanisms of this damage are urgent issues today. In this paper, the current status and background of rice ripening damage by high temperatures are shown. Furthermore, the studies on the mechanisms of grain weight decrease, poor palatability, cracking grain and immature grains with white portion and deep ditch and also the studies on the improvements of tolerant cultivars and cultivation methods are shown and discussed for future works.