A series of air temperature (Ta) and relative humidity (HR) measurements were carried out in five urban parks and their surroundings in Mexico City. It was found that Ta is lower and RH is higher inside the parks. There were differences (P less than 0.05) between the parks and surroundings in air temperature, relative humidity, vapour pressure (e), vapour pressure deficit (VPD) and the thermohygrometric human comfort index (THI). Ta differences were more marked during the early afternoon. Maximum differences of Ta, e, and DPV were 5.6 degrees C, 0.6 and 1.2 mbar. There is strong evidence that the magnitude of differences in Ta are directly proportional to the surface of urban parks.