We determined the phenolic and total fl avonoid contents and some physiological characteristics (water potential, chlorophyll fl uorescence, chlorophyll index) of Paeonia lactifl ora Pall., growing in the Botanical Garden, Mongolian Academy of Sciences. Cultivated plants were harvested at the beginning of vegetation (May), fl owering (June), seed formation (July), seed dispersal (August) and end of vegetation season (September). Phenolic content in leaf and stem was increased during the vegetation period and the highest level was reached during the seed formation stage, and it decreased at the end of the vegetation stage. On the contrary, the total fl avonoid content in leaf and stem is decreased linearly as the development stages advanced and the highest level was observed at the fl owering stage. Variations of water potential, chlorophyll fl uorescence and chlorophyll index of cultivated P. lactifl ora, increase at the beginning of vegetation and fl owering stages, and decrease from seed formation stage to end of the vegetation stage. Oyungerel, Sh., Batzaya, G., Byamba-Yondon, G., Lyankhua B., Ochgerel, N., Usukhjargal, D. 2017. Seasonal variation of some bioactive compounds and physiological characteristics in peony (Paeonia lactifl ora Pall.). Mong. J. Biol. Sci., 15(1-2): 47-51.