Abstract: The objective of this study is to ascertain the temporal and spatial differentiation of land use conversion in Northeast China, determine their causes, and analyze their environmental impacts. Also elucidated is the role of institutional constraints in these changes during agrarian restructuring in the 1990s when market was hybridized with the planned economy. Six land use types were mapped from TM images recorded in 1990, 1995 and 2000. Overlay of these maps in ArcInfo revealed that farmland and grassland decreased by 4.99×10⁴ and 1.40×10⁴ hm², respectively, while water, built-up areas, and woodland increased by 2.39×10⁴, 1.93×10⁴ and 1.44×10⁴ hm², respectively. Over three-quarters of these changes occurred from 1990 to 1995. Farmland changed mainly to woodland, water and built-up areas while woodland and grassland were converted chiefly to farmland. Spatially, the change from woodland to farmland adjoined the margin of natural forests while the change in the opposite direction was restricted to the agro-pastoral west. Paradoxically, reclamation of grassland as farmland also took place here. Besides, fallow land here was changed to grassland and to farmland in the Three River Plain. Driven by market demand and government regulation, rice was cultivated more widely with the creation of 338803 hm² paddy out of non-irrigated field. However, lack of water forced 40230 hm² paddy field to degenerate into dry land. These chaotic and conflicting changes were caused largely by lack of stability and consistency in land use policy. While climate warming made some of these changes possible, they have caused such environmental problems as land degradation, increased flooding and mini climate change.