Sowing date and seedling age had important effects on the growth, development and yield formation of rice. To clarify the differences in root growth of rice with long seedling ages and their responses to sowing dates, experiments were conducted using two rice varieties, Xingengyou 1 and Zhengdao C42. Two sowing dates, May 8 and May 18(denoted as S1 and S2), were set, and two seedling ages, 30 d and 40 d(denoted as T30 and T40), were established under each sowing date. Measurements were taken of rice yield, root length, root volume, active root absorption area, total root absorption area, root oxidation activity, as well as the contents of zeatin and zeatin riboside(Z+ZR), abscisic acid(ABA), and organic acids(acetic acid, tartaric acid, oxalic acid, citric acid) in root bleeding sap. The results showed that with delayed sowing date, root length, root volume, active root absorption area, total root absorption area, root oxidation activity, Z+ZR content, acetic acid content, tartaric acid content and yield of long-seedling-age rice in all growth stages(except at the tillering stage) exhibited decreasing trends, and all indices of the two tested varieties reached the lowest values under S2T40. Compared with S1T30, at the heading stage, root length, root volume, active root absorption area, total root absorption area, root oxidation activity, Z+ZR content, acetic acid content, tartaric acid content and yield of Xingengyou 1 under S2T40 decreased by 52.7%, 32.0%, 30.8%, 52.7%, 35.0%, 9.1%, 79.8%, 79.2% and 47.3%, respectively; those of Zhengdao C42 under S2T40 decreased by 54.5%, 11.3%, 2.9%, 54.5%, 30.3%, 16.3%, 26.6%, 79.4% and 21.0%, respectively. ABA, oxalic acid and citric acid contents increased with prolonged seedling age, and ABA and citric acid contents of both varieties reached the highest values under S2T40. Compared with S1T30, at the heading stage, ABA and citric acid contents of Xingengyou 1 under S2T40 increased by 3.6% and 26.3%, respectively; those of Zhengdao C42 under S2T40 increased by 11.0% and 58.1%, respectively. In conclusion, under different sowing dates, long seedling age reduced root length and root volume, inhibited root physiological activity, Z+ZR synthesis, and secretion of acetic acid and tartaric acid in root bleeding sap, and increased contents of ABA, oxalic acid and citric acid. These changes consequently resulted in significant reductions in panicle number, seed-setting rate and grain weight, and ultimately led to yield loss.