Abstract: Salicylic acid (SA), acetylsalicylic acid (ASA), and 14-hydroxylated brassinosteroid (HBR) are natural, endogenous plant growth regulators with high efficacy. Spraying those exogenous substances can effectively alleviate the adverse effects of heat stress in rice, but its physiological mechanisms, and the quantitative effects on increasing rice yield are still unclear. In this study, the dominant rice variety in Jiangxi Province ‘Jingliangyouhuazhan’ was used to investigate these aspects. A 2-year (2020, and 2021) experiment was conducted involving four sowing dates (April 25, May 5, May 15, and May 25) to investigate the effects of application of SA, ASA and HBR, and the sowing date on the physiological characteristics, and yield of rice subjected to high temperature stress. Under ambient high temperature conditions (daily average temperature ≥ 30 ℃ for ≥ 3 days or daily maximum temperature ≥ 35 °C for ≥ 3 days), 0.50 mmol·L⁻¹ SA, 0.50 mmol·L⁻¹ ASA, 0.20 μmol·L⁻¹ HBR, and their combinations (SA+HBR, and ASA+HBR) were applied to leaves from the late booting-stage to the flowering stage, with clean water as a control (CK). Compared with the CK treatment, rice plants treated with SA, ASA, HBR, SA+HBR, and ASA+HBR had a significantly higher soluble sugar content, soluble protein content, proline content, relative chlorophyll content (SPAD value), superoxide dismutase activity, peroxidase activity, and catalase activity (P<0.05) but a significantly lower malondialdehyde content (P<0.05) in flag leaves. Compared with the CK treatment, the SA, ASA, HBR, SA+HBR, and ASA+HBR treatments significantly increased the number of differentiated spikelets per panicle (P<0.05), but significantly decreased the degenerated spikelet percentage (P<0.05) under high temperature conditions. Compared with the CK treatment, the SA, ASA, HBR, SA+HBR, and ASA+HBR treatments significantly increased the number of grains per panicle, and actual yield (P<0.05) under high temperature conditions, and increased the seed-set rate. Moreover, compared with the CK treatment, the number of grains per panicle and actual yield increased on average by 5.01% and 5.69% under the SA treatment, by 4.40% and 4.00% under the ASA treatment, by 5.94% and 7.95% under the HBR treatment, by 8.15% and 12.30% under the SA+HBR treatment, and by 6.73% and 10.3% under the ASA+HBR treatment, respectively. Interestingly, the ranking of comprehensive evaluations of rice physiological indicators of the five treatments was as follows: SA+HBR > ASA+HBR > HBR > SA > ASA > CK. Compared with plants sown on April 25 and May 5, plants sown on May 15 and May 25 had suitable temperature conditions, such as a higher accumulated temperature with average daily temperature ≥ 10 ℃. In addition, the late sowing reduced average daily temperature, number of days during which daily average temperature was ≥ 30 ℃, and number of days during which daily maximum temperature was ≥ 35 ℃ from the late-booting stage to the mature stage. Under the CK treatment, the mean values of number of grains per panicle and actual yield under the last two sowing dates (May 15 and May 25) were higher than those under the first two sowing dates (April 25 and May 5), with average increases of 9.13% and 7.98%. Therefore, the application of SA, ASA, HBR, SA+HBR, and ASA+HBR, and the use of an optimal sowing date (from May 15 to May 25) increased the single-season rice yield under high temperature conditions.