Abstract: Changes in the species diversity and productivity of grass communities along altitudinal gradients and the relationship between diversity and productivity are important issues in ecology, and can explain variations among functional groups. The aim of this study was to determine the variations in the species diversity and productivity, and the factors affecting them, in the alpine meadow ecosystem. Field surveys of alpine meadows were conducted at four different altitudes (around 4485, 4535, 4585, 4635 m) in northern Tibet. Plant biomass and species composition were determined, and diversity indexes were calculated from the data. The productivity increased then decreased with rising altitude, and the highest productivity was around 4535-4585 m. In terms of functional groups, sedges moved from a comparative advantage to an absolute advantage as the altitude increased, while forbs and grasses became less important at different rates. Legumes became more important and then less important as the altitude increased. The species richness, Simpson index, Shannon-Wiener index, and Pielou evenness index were significantly higher at middle altitudes than at higher and lower altitudes (P>0.05), leading to a hump-shaped curve in plots of species richness vs. altitude and diversity vs. altitude. There were positive correlations between biomass and the Shannon-Wiener index and between biomass and the Simpson index (P<0.05), but not between biomass and the Pielou evenness index or biomass and the importance of functional groups (P>0.05). These findings indicate that the productivity and diversity of alpine meadows in northern Tibet are strongly influenced by altitude, which is related to variations in many environmental factors. This information will be useful for developing strategies to manage and preserve this important ecosystem.