Abstract: The IAA-Leucine Resistant1-like Hydrolase（ILL）genes is thought to regulate the release of free indole-3-acetic-acid（IAA）which is involved in the regulation of fruit development and others developmental processes. In order to further study the function of ILL family genes in peach，the member number of ILL gene family was confirmed；Thereafter their distribution on the scaffold，putative proteins，phylogenetic classification，and expression patterns were analyzed. We identified 9 ILL genes in the entire peach genome，which distributed across 4 scaffolds（1，2，3 and 7）. The members of the ILR1-like family genes were PpILR1，PpILR2，PpILR3，PpILR4，PpILL1，PpILL2，PpILL3，PpILL4 and PpILL5. All of their putative proteins contained M20 and M20 dimerisation domains. The relative expression levels in mesocarps of peach fruit at different developmental stages were also detected by quantitative real-time PCR. The results showed that several genes exhibited different expression patterns during fruit development.Moreover，the transcript level of PpILR1 was significantly up-regulated at the late-ripening stage.

Key words: Prunus persica, fruit development, IAA-Leucine Resistant1-like Hydrolase, indole-3- acetic-acid, melting-flesh