ABSTRACT Although enhancement of sink capacity with heavy-panicle is an important approach to the improvement of yield potential in super rice (Oryza sativa L.) breeding, environmental fluctuations may greatly affect fertilization and grain filling of heavy-panicle rice. Here, we investigated the response of heavy-panicle rice varieties to high temperature at flowering and grain filling stages under field conditions, with a focus on spikelets positions on the panicle. Six varieties each with four staggered sowings were grown under various climatic conditions, and thus their flowering stages and grain filling stages experienced high or normal temperature weather scenarios. When rice varieties grown under high temperature, spikelet fertilities increased in all tested varieties. Grain weights of varieties CW2221, K106 and R-2 under high temperature stress showed an average of 10.81% increase compared with normal temperature, whereas 'C418', 'J1307' and 'Xianghui210' decreased by 15.21%. Head milled rice rates significantly decreased, but chalky grain rates and chalkiness degrees significantly increased under high temperature. We further demonstrated that the effects of high temperature on spikelet fertility, grain weight and grain qualities were correlated with grain positions. These results indicate that understanding effects of high temperature on grain weight and quality in heavy-panicle rice varieties is a key factor for super rice breeding in the future.