The summer climate around the Tokyo metropolitan area has been analysed on an urban scale, and the regional characteristics of the thermal energy balance of a bayside business district in the centre of Tokyo (Otemachi) have been compared with an inland residential district (Nerima), using a mesoscale meteorological model incorporating an urban canopy model. From the results of the analysis, the mechanism of diurnal change in air temperature and absolute humidity in these areas is quantitatively demonstrated, with a focus on the thermal energy balance. Moreover, effective countermeasures against urban heat-islands are considered from the viewpoint of each region's thermal energy balance characteristics. In addition to thermal energy outflux by turbulent diffusion, advection by sea-breezes from Tokyo Bay discharges sensible heat in Otemachi. This mitigates temperature increases during the day. On the other hand, because all sea-breezes must first cross the centre of Tokyo, it has less of a cooling effect in Nerima. As a result, the air temperature during the day in Nerima is higher than that in Otemachi.