The effect of temperature on respiration and phoosynthesis wwere investigated in an ephemeral medicinal plant Ferula krylovii Korov in comparison with an non-ephemeral plant Peganum harmala L. In terms of the respiration rate based on the oxygen consumption per gram fresh leaf, an abrupt rise in respiration rate when the temperature was raised to 30 ℃ was observed in P. harmala, further temperature increase to 35 ℃ or above resulted in fast deactivation of the respiration system. The respiration rate at 45 ℃ reached 3.1 times high over that at 20 ℃. In contrast, through the entire tested temperature range, neither abrupt rises in respiration rate, nor fast deactivation of the respiration system was observed in P. harmala. In addition, even the respiration rate did not show significant change in response to the temperature change. This was an indication that the respiration system in F. krylovii was much more sensitive to temperature change and more vulnerable to higher temperatures compared with P. harmala. On the other hand, the photosynthetic rate of leaves in F. krylovii increased steadily to a maximum with the rise in temperatures from 20 to 35 ℃ and was constantly higher than that of leaves in P. harmala. in this temperature range, but the photosynthetic system showed fast deactiviation within a few minutes when the temperature was raised to 40 ℃ and above. On the contrary, the photosynthetic rate of leaves in P. harmala. reached its height at 40 ℃, declined slightly at 45 ℃, but a close linear rate was kept and no sign of photosynthetic deactivation was observed, indicating that the photosynthetic system in P. harmala. was highly resistant to higher temperature stress. Because either the respiration or the photosynthetic system was all more sensitive to higher temperatures in F. krylovii than in P. harmala, this sensitivity may be one of the main reasons leading to the dormancy of F. krylovii in early summer.