Global temperatures are now predicted to be 1-6 ℃ warmer than today by the year 2100. Environmental warming is likely to have significant effects on plant carbon relations, particularly through its effects on photosynthesis and respiration. In terrestrial environments, the nighttime daily minimum air temperatures in recent decades have increased more than the daytime maximum air temperatures. Understanding how plants respond to differential day/night warming may help scientists to predict the responses of plants to global warming. Most published studies of the effects of warming on plant growth have focused on either dominant species or invasive species. Little attention has been paid to endangered plants, but understanding how such species adapt in the context of global warming may be critical to their survival. Sinocalycanthus chinensis is an endangered plant belonging to the family Calycanthaceae. Here, we analyzed the effects of differential simulated day/night warming on the photosynthesis characteristics and chlorophyll fluorescence parameters of S. chinensis seedlings. Three different simulated day/night warming treatments were included in the experiment: 1) warming of 2 ℃ above ambient temperature at daytime; 2) warming of 2 ℃ at nighttime; 3) warming of 2 ℃ at both day- and nighttime. Seedlings exposed to ambient temperatures without warming were used as the control treatment. In three seasons, the net photosynthetic rate (A_net) and the maximum net photosynthetic rate (A_max) in all three warming treatments were higher than in the control, indicating that simulated warming could increase the photosynthetic ability ofS. chinensis. Simulated warming also increased the daily mean stomatal conductance (G_s) and the dark respiration rate (R_d), while it decreased the daily mean intercellular concentrations of CO₂. In three different seasons, A_net and A_max ofS. chinensis seedlings subjected to daytime warming were the highest, indicating that S. chinensis seedlings with daytime warming had the highest photosynthetic ability. The apparent quantum yield, light saturation point, and relative chlorophyll content of S. chinensis seedlings subjected to daytime warming were significantly higher than plants in the other warming treatments and the control. Simulated warming significantly decreased the F_v/F_m value of S. chinensis seedlings. During the period from 12:00 pm to 2:00 pm, the F_v/F_m value of S. chinensis seedlings treated with daytime warming was the highest, followed by those treated with nighttime warming and all-day warming, with significant statistical differences among the treatments. In conclusion, the different warming treatments increased the photosynthetic ability of S. chinensis to different degrees. The maximum values of A_net and A_max of S. chinensis seedlings subjected to daytime warming suggested that the highest photosynthetic ability of S. chinensis seedlings occurred under daytime warming. This might be due to the increase in relative chlorophyll content, the enhancement of the light adaptation ability, and the lower levels of light stress in the leaves of S. chinensis seedlings under daytime warming. The results of this study suggested that warming conditions in the future will improve the photosynthetic physiological activity and promote the growth of S. chinensis, perhaps benefiting this endangered species.