Abstract:The photosynthetic characteristics of Prinsepia unifloraBatal. were examined by using Li-6400 Portable Photosynthesis System. The results indicate that the diurnal curve of photosynthesis rate (Pn) of P. unifloraleaf presents two peaks, and the fist peak appeares at 10:00 ,and sub-peak at 15:00, with an obvious middepression. The diurnal curves of leaf transpiration rate and stomatal conductance are similar to Pn, with two peaks too. Pn is significantly positive related with transpiration rate and stomatal conductance.The principal environmental factors affecting Pn are photosynthetic active radiation and relative humidity. The light saturation point and light compensation point of P. unifloraare 1 020 μmol·m ^-2·s ^-1and 23.8 μmol·m ^-2·s ^-1respectively, while the apparent quantum yield is 0.056 9. The CO ₂saturation point and CO ₂compensation point are 1 330 μmol·mol ^-1and 54.7 μmol·mol ^-1respectively, while the carboxylation efficiency is 0.072 4. The optimal leaf temperature of photosynthesis is 24.9℃. The seasonal variation of Pn presents a twopeak curve too.