The research was carried out to examine how paddy fields could influence to the climate in the city. In 1993, the air temperature in Satte city of Saitama Prefecture in Japan was investigated both before and after the period of irrigation to the paddy fields. Each record was transferred onto the area map by introducing appropriate isotherms to illustrate a distribution pattern of the air temperature measured. From the aerial photographs, each representative point was confined to the center of the circle with a diameter of 500m and the ratio of the area covered by paddy fields (%) was calculated. To estimate the influence of the paddy fields to the city climate, the relation between air temperature and the land covering ratio of paddy fields was analyzed by the stratified sample regression analysis. The regression equations showed that the cooling effect of paddy fields remarkably changed from before to after the irrigation to the paddy fields. The estimate effect at 10% of the paddy fields covering ratio was 0.10°C before irrigating to the paddy fields, while 0.20°C after the irrigation completed.