Abstract:Diurnal changes of transpiration rate and stomatal conductance in Rhizophora stylusa Griff. mangrove forest and some ecological factors were determined by porometer in Hainan. In the sunny day in December, transpiration rate of the forest canopy reached its peak between 10 to 11 o'clock at 4. 27 - 4. 34μg · cm-2s-1, and decreased at noon. It was shown that the complex correlation between transpiration rate of community and ecological factors, i. e. , photosynthetic active radiation (PAR), leaf-air vapour pressure difference, air temperature, relative humidity and leaf temperature, was very significant. The critical factors affecting transpiration rate of the community were PAR, relative humidity and leaf-air vapour pressure difference. The everage of total transpiration rate of R. stylosa forest was 2502 g H2O · m-2d-1, of which the transpiration rate of the canopy accounted for 63%.