Abstract: Based on RS-derived maps and socio-economic statistics, this paper analyzed the spatio-temporal dynamic pattern and driving mechanism of built-up area expansion in Su-Xi-Chang region from 1990 to 2010. 3S-based spatial analysis techniques were used, landscape expansion indices were calculated, and multiple stepwise regression models were also used. In the past 20 years, the built-up area had experienced rapidmoderateaccelerating expansion stages, which was strongly affected by the national development strategies and policies regarding land use. During the study period, the built-up area had increased by 2218.9 km² mainly due to the encroaching from paddy field, dryland and artificial ponds. From 1990-1995, the pattern of builtup area expansion was dominated by the infilling and edge-expansion type; from 1995-2000, the outlyingtype had overplayed infilling and edge-expansion types due to policy restrictions on the latter; after 2000, the outlyingtype growth had decreased by a large extent, whereas the infilling mode had increased dramatically, which resulted in the spatially compact pattern of the newly built-up area. The increase of urban population and the boom of regional economy were the major driving forces of built-up area expansion. The study implied that improvements were urgently needed in land management system and high-efficiency use of cropland. Promoting the compact development of built-up area was also crucial for striving toward regional sustainability.