Urbanization process creates significant changes in land surface and atmospheric properties of location that affect the net amount of radiation received at ground level, relative humidity and sensible heat. Green space with a variety of different land uses in different parts of city creates variety of heat flow that creates the framework of microclimate. Expanding population and industry growth in the Isfahan metropolitan city and its combination with natural factors cause changes in the climate of this city.The purpose of this study was to identify micro-climate of Isfahan city and their effect on temperature, air humidity and reference crop evapotrairation in order to optimal management of landscape irrigation. Air temperature and relative humidity in the city was affected by various factors, including landscape surfaces, asphalt surfaces, building surfaces, agricultural lands, arid lands, water surfaces, population density and traffic.In order to investigate the effect of air temperature and relative humidity a GIS map of Isfahan city was used and five regions with different surfaces, were identified.Weather shelters and stability devices were installed ineach of five regions to measure air temperature and relative humidity. In order to justify the weather data from stability devices installed in the city with weather data from Isfahan meteorological station, a stability device was placed in the weather station (Reference station). Air temperature and relative humidity were measured with time interval of 5 minutes and period of 12 month from November 2010 to October 2011. Daily reference crop evapotrairation was calculated using FAO-Penman-Monteith and Hargreaves-Samani equations. Analysis was done in the four periods from 0 to 6, 6 to 12, 12 to 18 and 18 to 0 using recorded data. Air temperature and relative humidity in each of five stations located in the city were defined as a linear function of air temperature and relative humidity in the reference station. The results showed that there is a significant differences (P 0.01) in all 12 months of the year for air temperature and relative humidity between city stations and reference station. Maximum difference in average monthly air temperature was equal to 6.07° C between reference station and station 3 (Fadak Garden) in September and maximum difference in average monthly relative humidity was equal to 40.73% between reference station and station 1 (Flowers Garden) occurred in December. The most effect of urban microclimates was observed on the minimum daily air temperature in all stations. Maximum difference in air temperature between city stations and reference station and relative humidity at city station and reference station has occurred at night and minimum difference has occurred at day. Air temperatures during the day in downtown station were more than reference station in all months of the year. The type and extent of green space has a great impact on air temperature and relative humidity. Green space surfaces including parks and lawns with reducing hard surfaces cause decrease in air temperature and increase in relative humidity. Green canopy of trees planted along streets has a little effect on reducing air temperature and increasing relative humidity. Because the land uses under the canopy of trees is different and has interaction effect with green space. Maximum difference in water requirement calculated using the FAO - Penman - Monteith equation between reference station and the city stations was 11 percent.