Abstract: To ascertain the influence mechanism of high temperature after anthesis on rice quality, taking two rice lines including heat- tolerant line 996 and heat- sensitive line 4628 as materials, an experiment was conducted in growth chambers to investigate the effect of high temperature and optimal temperature after anthesis on rice appearance quality, milling quality, cooking and eating quality and starch granule structure of endosperm. The results showed that under high temperature after anthesis, ratio of grain length to width, chalky rate and chalkiness increased, milled rice rate, head rice rate, amylose content and gel consistency decreased, protein content increased. Under high temperature treatments, gelatinization temperature, final viscosity, set back and peak time increased, breakdown decreased, Mg content and K content increased, Mg/K ratio decreased. Under the same treatment, rice quality of heat tolerant line 996 was less affected by high temperature than that of heat sensitive line 4628. Under high temperature stress after anthesis, starch granule had an incompact arrangement, most of the starch granule existed in the form of a single starch endosperm, refractive index decreased, transparency reduced, and led to the formation of chalk. Under high temperature after anthesis, the increase of protein content, the decrease of Mg/K, the change of rice RVA characteristics and starch granule structure of endosperm could be the main reason of the decrease of rice cooking and eating quality and appearance quality.