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The quantification of changes in long-term trends in grassland net primary productivity (NPP) and its large-scale driving forces are important for understanding terrestrial ecosystem changes in arid and semi-arid regions. Based on the MODIS-NPP dataset, this study investigated patterns in the spatiotemporal variations in NPP and its possible influencing factors in Inner Mongolia during 2000-2014 using the linear trend analysis method, correlation analysis, and an F test. The results show that grassland NPP had an annual rate of increase of 4.53 g C/(m(2).a) with a significant increasing trend (p < 0.01). Spatial analysis results indicate that the average grassland NPP presented a gradual increasing trend from southwest to northeast, with an area of longitudinal zonality being identified. Grassland NPP presented a significant increase (p < 0.05) in more than 31.93% of the region. Grassland NPP and growing season precipitation (GSP) had a significant negative correlation in 54.78% of the study area. Grassland NPP and the growing season average land surface temperature (GSALST) had a significant negative correlation for 65.93% of the study area; growing season average temperature (GSAT) had no significant effect on the grassland NPP. For different grassland types, GSP had the greatest impact on alpine meadows (r = 0.73), and GSALST had the greatest impact on alpine steppes and alpine meadows (r = - 0.81). Related ecological restoration projects such as fenced rangeland and planted grass played a positive impact on annual NPP in the study area.