The summer climate in Osaka city is very hot and humid, and maybe the most intense thermal environment in Japan. The artificial heat released from human activities and the earth surface materials with large heat capacity are main causes on the deterioration of thermal environment in urban summer night. These urban effects are analyzed using the observed data in Osaka city through the comparison of air temperature variation with the places 1) in the urban center, in the large park and in the suburban area, and 2) between weekday and holiday. The air temperature data observed at the following places were used; 1) on the roof of two different office buildings as the typical data of urban center, 2) in the flower garden in Osaka castle park, 3) the elementary school where is 9km apart from urban center as the typical data of suburban area, and 4) Osaka Meteorological Office. The amplitude of air temperature in "urban" was small comparing with "park" and "suburban". It seems that the differences of amplitude were caused by mainly the difference of heat storage. The air temperature in "urban" does not fall around midnight in weekday, whereas it continues to fall in holiday. It is estimated that it is caused by artificial heat released. However even in holiday morning, the minimum temperature in urban center was 2-3C higher than in "park". It seems that the influence of heat storage is larger than artificial heat released, because the temperature difference between "urban" and "park" appeared even in holiday night as well as in weekday. It is needed directly to measure the atmospheric radiation, because the cloudiness affects to the air temperature directly, and there are no continuous observed data.