Abstract: The physiological responses of Ceiba pentandra and Bombax ceiba to temperature increase were studied with half-year-old seedlings. The results showed that the relative electrical conductivity of C.pentandra and B.ceiba increased with the increase of temperature, and the semi-lethal high temperatres of them were 47.4 ℃ and 49.6 ℃, respectively. For C.pentandra, chlorophyll b and chlorophyll (a + b) increased significantly at 45 ℃, and carotenoid content increased significantly from 37 ℃. The chlorophyll content and composition of B.ceiba did not vary significantly with the increase of temperature, but the carotenoid content also increased significantly from 37 ℃. F_o increased and F_m and F_m/F_v decreased significantly for both the tree species at 45 ℃, but the variation of all the indexes mentioned above were greater in C.pentandra than those in B.ceiba. The content of malondialdehyde (MDA) in both of C.pentandra and B.ceiba not significantly increased with the increase of temperature, and MDA increased by a greater extent in C.pentandra. The content of soluble sugar and proline in C.pentandra and content of soluble sugar in B.ceiba did not vary with the increase of temperature, but the content of proline increased significantly in B.ceiba. In conclusion, the thermotolerance of B.ceiba is higher than that of C.pentandra, and they might adopt different mechanisms to cope with the increasing of temperature.