Abstract: The characteristics of photosynthetic physio-ecology in leaves of Heptacodium miconioides seedlings had been studied. The results showed as follows: (1) The diurnal variations of net photosynthetic rates (Pn) and transpiration rates (E) were "twin-peaked" curve. The diurnal variations of internal CO₂ concentration (C_i) were just opposite to Pn. The increasing of C_i at midday showed that the decreasing of Pn were related to non-stomatal restriction factors. Respiration rates (R) were highest at midday, whose diurnal variations were "single-peaked" curve. The diurnal variations of stomatal resistance (r_s) were just opposite to E. Solarenergy utilization efficiency (SUE) increased gradually in the afternoon, which was highest at 7:00 in the morning and lowest at midday. Water utilization efficiency (WUE) was highest at 7:00 and lower during 10:00～16:00. (2) The experiments of response of Pn to light indicated that saturated light intensity and apparent quantum yield (AQY) were highest in morning and lowest at midday. Light compensation points (LCP) were nearly in the morning and in the afternoon, but whose increasing had more than doubled at midday. Edecreased under shad at different time, the most decrea sing of Ewere in the afternoon, on the contrary, r_s increased at the same time. (3) Carboxylation efficiency (CE) were highest in the morning and lowest at midday, while CO₂ compensation points (CCP) were highest at midday.