Mornya, P. M. P. and Cheng, F. 2011. The levels of hormone and carbohydrate in autumn and non-autumn flowering tree peonies. Can. J. Plant Sci. 91: 991-998. This study analyzed the levels of gibberellic acid (GA₃), indole-3-acetic acid (IAA), cytokinin (CTK) and abscisic acid (ABA) hormones using high-performance liquid chromatography, along with the levels of sucrose, reducing sugar and starch carbohydrates by spectrophotometer during induction, initiation and differentiation stages of bud development in autumn (AFP) and non-autumn (NAFP) flowering tree peony cultivars exhibiting variations in flowering pattern. The experimental design was a randomized complete block with three replications. The variation in flowering pattern between AFP and NAFP was largely influenced by differences in GA₃, IAA and CTK levels at different bud developmental stages. The flower formation cycle was completed earlier in AFP than in NAFP, hence flowering was twice annually. Cytokinin, particularly N6-(▵2-isopentenyl)-adenosine (iPA), could be a critical hormone in autumn flowering of tree peony, as its differences in levels between AFP and NAFP remained significant across bud developmental stages. However, only GA₃ had negative differences across bud developmental stages, indicating that GA₃ levels were consistently higher in NAFP than in AFP, but the reverse holds true for CTK. The differences in GA₃, IAA and CTK between AFP and NAFP were significant (P<0.05) for at least two-thirds of the bud developmental stages. Carbohydrates may not significantly influence the flowering pattern of tree peonies. Autumn flowering in tree peonies could therefore be achieved by regulating GA₃, IAA and CTK levels, particularly at the induction and initiation stages of bud development to facilitate the completion of the floral formation cycle, well in advance of bud dormancy period. The findings of this study could lay the scientific basis for genetic engineering of flowering pattern of tree peonies.