Understanding how the seed yield and seed quality respond to global warming is crucial for understanding how new grassland establishment responds to global change. This study evaluated Leymus chinensis, a dominant perennial grass widely distributed in the eastern regions of the Eurasian grassland zone, as a model to investigate the effect of increasing ambient temperature on seed production, seed mass, germinability, and subsequent seedling growth. As the temperature rose, there were significant reductions in the number of flowering plants and in seed number per square metre but significant increase in the number of florets and the number of seeds per plant. Increasing temperature decreased the proportion of light weight seeds, increased the proportion of heavy weight seeds and led to a significant increase in the mean dry weight. Germination success, germination rate and the root : shoot ratio of light weight seeds were reduced, while heavy weight seed did not appear to be affected by elevated temperatures. Finally, germinating seeds per unit area was reduced by increased temperature. The reduction in the number of germinating seeds with increasing temperature implies that continued global warming will further constrain new grassland establishment of L. chinensis in the eastern regions of Eurasia.