Background <p>Forage quality is a fundamental determinant for livestock productivity in natural grasslands, and is sensitive to the variations in climate, soil, and plant community composition. However, the contributions of those factors to the regional variation of forage quality largely remain unclear. We examined forage quality of 45 alpine meadow communities over a 23.6 × 10⁴ km² area on the eastern Qinghai-Tibet Plateau in China. We also&#xa0;examined the variations and drivers of multiple forage quality indicators across regional scale.</p> Results <p>The results showed that the natural grasslands in this region had high crude protein and non-fiber carbohydrates content, and relative feed value, but low-fat content. Forage quality of forb-dominated grasslands was higher than grass- and sedge-dominated&#xa0;ones. There were substantial geographical variations of forage quality, which decreased with increasing longitude, and increased with increasing latitude and altitude. Climate and plant community composition directly controlled the geographical patterns of forage quality. Climate had larger contribution to forage quality than soil and plant community composition. Less sedge and more forb in community resulted in higher forage quality. Forage quality was higher in sites with colder, drier and more variable climate. Soil conditions indirectly affected forage quality by mediating the plant community composition.</p> Conclusions <p>This study highlights the role of climate in driving the variation of forage quality in the alpine grasslands. The findings could provide scientific supports for grassland management and sustainable development on the Qinghai-Tibet Plateau.</p>