Abstract: Abstract: Severe soil loss has caused ecological degradation for the global ecosystem, thus it is a major problem facing the world today. Timely and fast monitoring ecological changes in soil loss regions has become an increasing concern. This paper develops a remote sensing assessment method of soil erosion-induced changes in regional ecological quality based ecological index (RSEI). The proposed index combines four indicators from existing remote-sensing indices/components to represent greenness, dryness, wetness and heat, which are the important ecological indicators frequently used in assessing regional ecological status. The four remote-sensing indices/components are the normalized difference vegetation index (NDVI), soil index (SI), wetness component of the tasseled cap transformation (Wet), and land surface temperature (LST). The principal component analysis (PCA) was utilized to compress the four indicators into one index - RSEI, in order to assess overall ecological status. The new index, RSEI, was thus constructed using the first component as it was proved to have effectively combined the most information of the four indicators. The application of the RSEI in Hetian basin area in Changting county of Fujian province, one of the most serious reddish soil erosion areas in southern China, showed that the RSEI can quantitatively assess the ecological effects of soil loss treatment in the area and easily detect spatial and temporal changes of the ecological quality through a time period from 1988 to 2010. The application utilized three Landsat TM images of 1988, 2004 and 2010. The four indicators (NDVI, SI, Wet and LST) of each year were retrieved from the images and then combined through the PCA transform to form the RSEIs for the study years. The RSEI-based analysis indicated that after a more than 20 years fight for soil loss in the area by the local people and government, the ecological quality of the area has been significantly improved. This is suggested by an increase in the mean RSEI value from 0.5 in 1988 to 0.59 in 2010, accompanied by a decrease in low level RSEI area from 66.1% to 47.7%, and an increase of high level RSEI area from 33.9% to 52.3% in this duration. Quantitative analysis reveals that the greenness indicator represented by NDVI contributes most to the RSEI change among the four indicators used for generating the index. This suggests that the biological restore of soil erosion areas by planting tree and grass is an effective way to soil-erosion treatment for Hetian basin.