Net primary productivity (NPP) of South Jiangsu in 1999 and 2008 was estimated through CASA model, the spatial and temporal variations of NPP and its response to land use cover/change (LUCC) was also analyzed. The result showed: 1) from 1999 to 2008, NPP of South Jiangsu changed greatly both in space and time. 2) On regional scale, NPP of all 19 counties decreased: NPP of Kunshan reduced to the maximum of 242.04 g/m2, while Yangzhong reduced the minimum of 70.94 g/m2. High value area of NPP reduction was in Taihu basin and the low value zone was located in the northwest of South Jiangsu. 3) On land use scale, the average NPPs of six types were in decline: construction land and farmland decreased greatly with decline rates 55.69% and 45.74% respectively. In the high value area of NPP reduction, the conversion between farmland and construction land was most prominent while the NPP reduction in low value area was mainly due to the transformation between forest and grass land. This phenomenon was inconsistent to land use in city group of Taihu basin. The correlation between NPP change and farmland change was highest to 0.523. NPP loss and gain were great in four conversion modes: forest-water, farmland-water, forest-grassland and farmland-grassland.