Abstract: Evapotranspiration (ET), a link between hydrological and ecological processes, is very important to the stability of terrestrial ecosystems. In arid and semi-arid regions, where more than 90% of the effective precipitation is consumed by ET, variations in ET processes may weaken the stability of a grassland ecosystem plagued by water stress. Ningxia is located in the north China farming-grazing transitional zone; long term excessive conversion to farmland and overgrazing have greatly decreased the ecological function of the grassland ecosystem and generated serious changes in ET processes. Background information on grassland ET in the region is unknown, due to inadequate research on the characteristics of ET in undisturbed grassland in Ningxia. Research on the ET characteristics of grassland ecosystems within fragile ecological environments are important for regional agriculture and animal husbandry development, ecological restoration and reconstruction, and the construction of eco-barriers. This study, based on MOD16 ET data, corresponding climate data and grassland type, analyzed the spatial-temporal changes in ET in Ningxia from 2000 to 2014 and predict future trends. Regression analysis, correlation analysis and rescaled range analysis were employed. The results indicated that during a recent 15-year period (2000-2014), the ET of grassland increased (with fluctuations) and average ET was 228.03 mm per year. The upward trend was not significant (P>0.05) because of regional differences in precipitation and heat, and the annual and monthly ET of various grassland types presented obvious heterogeneity. The annual average ET also had a strong spatial heterogeneity (135.84-732.12 mm), higher ET in the south and lower in the north, but the fluctuation was small. More specifically, grassland ET mainly presented a decreasing pattern from north to south in northern Ningxia, and increasing from north to south in central and southern Ningxia. However, the variation in ET is small and the change is not significant in most of the study area. In the future, the increasing trend of ET in the grasslands will probably become significant and only small parts of the grassland system will experience reduced ET. Precipitation was the main factor determining the distribution pattern and inter-annual fluctuation of ET in grassland in Ningxia. Nevertheless, the influence of land use change caused by human activities in ET cannot be ignored.