Abstract: The accuracy validation of the MODIS/FAPAR product is a prerequisite for using it to estimate local net primary production (NPP), and to supply service for monitoring the balance of region carbon and arranging production of grassland animal husbandry rationally. For this purpose, we designed and carried out in-situ measurements of FAPAR in two 2 km×2 km areas within the temperate meadow-steppe grassland in Hulunber during growing season in 2008, and analyzed heterogeneity of the two sites using image of Beijing-1 satellite with resolution of 32 m, and then scaled up and validated MODIS/FAPAR products with in-situ measured data in grassland area. The results showed that the MODIS FAPAR product reflected very well the seasonal dynamics of in-situ FAPAR, but tended to overestimate the value with averaged relative error of 13.7% in the Stipa Baicalensis site and 18.7% in the Leymus Chinensis site. The MODIS/FAPAR algorithm was derived based on the global land cover map, which may be too broad for local areas. More fieldworks for various types of the grasslands are necessary.