Based on RS and GIS,the data of land use changes in Lanzhou City were extracted from TM,ETM,and thematic vector data from 1990 to 2006.Land use changes during the 16 years were analyzed and ecological environment effects were quantitatively estimated.Results showed that great changes in the city happened from 1990 to 2006.The area of woodland was increased significantly,most of which was transferred from grassland and cultivated land.The next was city traffic land,transferred from cultivated land,woodland,and unused land.The most significant reduction in land use was grassland which was transferred to cultivated land,woodland,and city traffic land.The total ecological service value of Lanzhou City rose from 43 594.95 million yuan in 1990 to 44 084.16 million yuan in 2006.These indicate that the environment of the city is developing toward a healthy status.