The Urban Heat Island (UHI) effect is particularly concerning in Mediterranean zone, as climate changeand UHI scenarios foresee a fast growth of energy consumption for next years, due to the widespread ofair conditioning systems and the increase of cooling demand. The UHI intensity is thus a key variable forthe prediction of energy needs in urban areas.This study investigates the intensity of UHI in Barcelona (Spain), the densest Mediterranean coastalcity, and its impact on cooling demand of residential buildings.The experimental analysis is based on temperature data from rural and urban Weather Stations andfield measurements at street level. The maximum average UHI intensity is found to be 2.8¿C in winterand 1.7¿C in summer, reaching 4.3¿C at street level. Simulations performed with EnergyPlus indicatethat the UHI intensity increases the sensible cooling load of residential buildings by around 18%–28%,depending on UHI intensity, amount of solar gains and cooling set point.In the light of the results, the UHI intensity in Mediterranean context should be properly consideredin performing energy evaluations for urban contexts, since standard meteorological data from airportweather stations are not found to be accurate enough.