Accurate global land cover (GLC), as a key input for scientific communities, is important for a wide variety ofap-plications. In order to understand the current suitability and limitation of GLC products, the discrepancy and pixel-level uncertainty in major GLC products in three epochs are assessed in this study by using an integrated uncertainty index (IUI) that combines the thematic uncertainty and local classification accuracy uncertainty. The results show that the overall spatial agreements (Aovalues) between GLC products are lower than 58％, and the total areas of forests are very consistent in major GLC products, but significant differences are found in different forest classes. The misclassification among different forest classes and mosaic types can account for about 20％ of the totaldis-agreements. The mean IUI almost reaches 0.5, and high uncertainty mostly occurs in transition zones andheterogen-eous areas across the world. Further efforts are needed to make in the land cover classifications in areas with highun-certainty. Designing a classification scheme for climate models, with explicit definitions of land cover classes in the threshold of common attributes, is urgently needed. Information of the pixel-level uncertainty in major GLC products not only give important implications for the specific application, but also provide a quite important basis for land cover fusion.