【Objective】 The objective is to clarify the genotype-dependent alteration in rice leaf senescence process and its relationship with the endogenous IAA content and its conjugated status in flag leaves during filling stage, and also to investigate the effect of N supply levels on leaf senescence and its relation to the endogenous IAA content and its conjugated status in leaves for different rice genotypes. 【Method】 Two rice genotypes, namely, the premature senescence mutant in flag leaf (psf) and its wild type (Zhehui 7954), were used to compare their difference in the temporal patterns of IAA content and its conjugated status as well as transcriptional expression of YUCCAs family genes in flag leaf during filling stage. Three N levels, including low nitrogen level (LN, 1.45 mmol/L), normal nitrogen level (MN, 2.9 mmol/L), and high nitrogen level (HN, 5.8 mmol/L), were designed to examine the response of IAA content and its conjugated status in senescent leaves to different N supply levels. 【Result】The free IAA content in the flag leaf of psf mutant was significantly lower than that of its wild type during leaf senescence, while the opposite was true for the genotype-dependent alteration in the conjugated status IAA (IAA-ASP) content in senescent leaves, with a markedly higher level and more rapidly increase of IAA-ASP content in the flag leaf of psf mutant relative to its wild type along with leaf senescence. Among 7 YUCCAs isoform genes related to IAA biosynthesis, the transcriptional expressions of YUCCA2, YUCCA3, YUCCA4 and YUCCA6 were relatively lower in the flag leaf of psf mutant compared with its wild type, with the down-regulated temporal pattern during leaf senescence, regardless of rice genotypes. However, the transcript amount of YUCCA7 in senescent leaves increased markedly from 0 to 21 days post anthesis, followed by a declining level of transcriptional expression at the late stage of leaf senescence process. This result implied that the rapid decrease in chlorophyll contents and also its accelerated leaf senescence symptoms for psf mutant were partly attributable to the weaker IAA biosynthesis in psf leaves during leaf senescence, in which the transcriptional level of YUCCA7 expression might play an important role in the regulation of IAA biosynthesis in senescent leaves; the effect of N supply on the endogenous IAA content and its conjugated status in rice leaves was greatly variable, depending on the stage of leaf senescence. At the initial and early stages of leaf senescence, LN treatment decreased the free-IAA content in rice leaves and increased the IAA-ASP content in rice leaves, while HN resulted in a marked increase in free-IAA content in the senescent leaves, with a significant decrease in IAA-ASP content under HN. Comparatively, HN treatment displayed lower level in both free-IAA and IAA-ASP contents than NN an LN treatment at the late stage of leaf senescence (for psf mutant at about 28 day post anthesis) with severe leaf senescence symptom【Conclusion】The onset and progression of leaf senescence were closely associated with IAA content and its conjugated status in rice leaves. The markedly increased IAA-ASP content in rice leaves may be considered as one of most important reasons for the accelerating progression of leaf senescence symptom, and HN-induced decrease in IAA-ASP content in rice leaves was, at least partly, responsible for the delay of leaf senescence progression.