ABSTRACT: To better understanding the genetic and physiological changes behind the dormancy process in tree peony, we performed customized cDNA microarray to investigate gene expression profiling in tree peony M-bM-^@M-^XFeng Dan BaiM-bM-^@M-^Y buds during chilling induced dormancy release. Endo-dormant tree peony plants were exposed to 0-4M-BM-0C from 5 November to 30 December 2009 in Qingdao, Shandong, China. Buds were collected after 0 d, 6 d, 12 d, 15 d, 18 d and 24 d chilling endured. DNA microarrays were customized using Agilent eArray 5.0 program, containing spots with 14,957 gene-specific 60-mer oligonucleotides representing 14,957 non abundant ESTs obtained from 454 sequencing normalized cDNA of tree peony buds during chilling duration (TSA, 65,217). Total 3,174 significantly differentially-expressed genes (P<0.05) were observed through endo-dormancy release, and the number of up-regulated (1,611) and that of down-regulated (1,563) was almost same. Expression of differentially-expressed genes associated with GA biosynthesis and signaling, cell growth and development was confirmed by quantitative RT-PCR, which displayed similar trends pattern in expression. Transcript profiling of tree peony was measured during chilling (0-4M-BM-0C) induced dormancy release. Mixed buds, three buds for each individual, were collected after 0, 6, 12, 15, 18 (endo-dormancy release), 24 days (eco-dormancy) chilling requirement fulfilling. Three replications (3 plants/ replication) were harvested between November and December.