Local residents of the Lhasa River Region (LRR) on the Qinghai-Tibetan Plateau in western China have noticed that the surrounding mountains have appeared conspicuously green since the 1980s. To verify these claims, we investigated trends of grassland activities in the LRR from 1982 to 2013 by using remotely sensed Normalised Difference Vegetation Index (NDVI) data, as a proxy for photosynthetic activity. Due to the limitation of available remote sensing data, we used long-term data with low resolution, GIMMS3g NDVI, to explore the temporal changes between 1982 and 2012; we used moderate resolution data, MODIS NDVI, to investigate the spatial variations of trends between 2001 and 2013. In addition, we examined the relationship between grassland change and climate change. The results revealed a significant upward trend in the annual mean NDVI of the LRR from 1982 to 2012, corroborating the observations of the local people. The increasing trend was more pronounced during the period of 1982-1999 than during the period of 2000-2012. The seasonal NDVI also exhibited a significant upward trend in spring and summer from 1982 to 1999. From the higher resolution MODIS NDVI data analysis, during 2001-2013, the lower regression slope values were mainly distributed in the river valley (the area of lower elevation), whereas the higher values pixels were located in the northern LRR (the area of higher elevation). In addition, the annual NDVI correlated significantly with temperature and precipitation during the study period. Temperature is a more significant factor influencing grassland change than precipitation in spring and autumn. However, the precipitation with the time lag effect is more significantly correlated with NDVI during the growing season (from May to October). The results of this project will help to monitor regional vegetation changes, understand the impact of climate change, and better manage the economically, environmentally and culturally significant grasslands of the LRR.