Measurement experiments were done in order to examine the effect of rooftop greening in suppressing surface temperature increases in summer. The thermal environment data, such as temperature, heat flux, etc., were continuously measured by machine. It was found that the rooftop surface temperature of the control section rose to over 50℃ at noon on clear days, while that of the vegetation section did not rise beyond 30℃. In this research, an indoor CFD was also executed to clarify the effect of rooftop greening. As a result, the energy required for air conditioning could be decreased by about 8% in summer.