In order to evaluate the effects of mitigating urban heat island by light and thin type rooftop greening system which could be applied in existent buildings, basic experiment about thermal characteristics of greening system were carried out. The results of heat balance analysis show the latent heat consumption of evapotranspiration at greening system to prevent increase sensible heat. But mitigating effects by greening system were varied in kind of plants, water condition and so on. Using evaporation efficiency as an index of evaporation ability, it is able to evaluate the difference of the effects by plants and water condition.
