Abstract: In order to explore the adaptation mechanisms of Stylosanthes guianensis to temperature stress, the responses of Chlorophyll fluorescence parameters and photosynthetic rates in leaves under low and high temperature stresses were studied. 40 days old seedlings were divided into three groups and transferred to growth chambers with different temperature treatments. The first group was subjected to temperature at 6℃ for 2 days as low temperature stress, the second group at 36℃ for 5 days as high temperature stress, and the third group at 25℃ for 5 days as the control. The experimental results showed that the chlorophyll fluorescence parameters(Fv/Fm, Ф_PSⅡ, qP) and photosynthetic rates in the leaves of S. guianensis decreased significantly as treated with cold stress, and were not affected under heat stress, which indicates that photosystem Ⅱ activity in S. guianensis was more sensitive to cold stress than heat stress. In addition, ATP content and activities of RuBPcase and FBPase in the leaves of S. guianensis were also decreased under cold stress, but it was not affected under heat stress. Therefore, sufficient ATP content in leaves perhaps can prevent decreasing photosynthetic rate in S. guianensis leaves.