High-temperature tolerance of two heat-tolerant rice cultivars (Ⅱ-you 838 and Shanyou 63) and two heat-sensitive rice cultivars (Ⅱ-you 63 and Teyou 559) was investigated by the HTTF (high-temperature tolerance identification of rice tiller under field conditions) method under natural high-temperature conditions between mid-July and late-August in Wuhan,Hubei Province.The results showed that the lowest seed setting rate (SSR) was observed at the hottest time point “2nd August”,and SSR of Ⅱ-you 838 and Shanyou 63 was significantly higher than that of Ⅱ-you 63 and Teyou 559,suggesting that high-temperature tolerance of cultivars Ⅱ-you 838 and Shanyou 63 was superior to that of cultivars Ⅱ-you 63 and Teyou 559,coinciding well with the practical performance of those cultivars.Similar results were obtained at time point “11th August”.The correlation and regression analysis showed that the SSR of tiller was negatively correlated with corresponding average temperature in flowering stage for all tested cultivars encountered by high-temperature stress,and the SSR of tiller of heat-sensitive cultivars Ⅱ-you 63 and Teyou 559 was much mo