Abstract: In the process of urbanization, much farmland has been changed into urban construction land, however, the non-market value of farmland is always be neglected. It is necessary to classify and quantify the ecological value of farmland. Taking Jiangsu Province as example, this paper classified the ecosystem service of farmland into four categories such as supplying, regulation, sustaining and culture. The value-appraising method was used to estimate ecosystem service value, loss of ecological value of farmland during process of farmland conversion. The results show that farmland ecosystem service value in Jiangsu Province is 213 859.9 Yuan·hm^-2, and its loss is 3 370 404.85 million Yuan from 1997 to 2004. Difference in environment and economy among different regions causes regional variation of farmland ecosystem service value in Jiangsu Province. The spacial distribution of farmland ecosystem service value characterizes reducing progressively from South Jiangsu to North Jiangsu. Finally, the paper suggests implementing ecological compensation mechanism, reconsidering farmland value, normalizing government behavior and innovation of appraising methods etc to protect farmland and properly estimate farmland ecological value.