The city is identified as altered natural environment by excessive changes in nature and increasing presence of manmade structures. Urban green spaces are remnants of nature in this environment and play an important role in ascending the level of life quality in the city. In this study the effects of urban sprawl on quantity of urban green spaces in region 2 of Tehran municipality were studied comparatively in 1989 and 2002 using aerial photos interpretations and geographical information systems (GIS). The studies indicate a considerable decrease in urban green spaces with a more intensity in the northern parts of the region. The sub-region 8th had the greatest amount of decrease among 9 sub-regions and 6th sub-region had the minimum rate of decrease. Two general strategies are concluded from the results of this study: 1) the priority of conservation and support of the existing green and open spaces 2) establishing new green spaces in some parts of the region which benefit less environmental quality.