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Mowing is an important land management practice for natural semi-arid regions. A growing body of empirical evidence shows that different mowing regimes affect the functioning of grassland ecosystems. However, the responses of plant functional traits to long-term mowing and their allometric scaling under long-term mowing are poorly understood. For a better understanding of the effects of mowing on grassland ecosystems, we analyzed the allometric traits of leaves and stems of Leymus chinensis (Trin.) Tzvel., a dominant grass species in eastern Eurasian temperate grassland, at different mowing intensities (no clipping, clipping once every two years, once a year and twice a year). Experiments were conducted on plots established over a decade ago in a typical steppe of Xilinhot, Inner Mongolia, China. Results showed that most of the functional traits of L. chinensis decreased with the increased mowing intensity. The responses of leaves and stems to long-term mowing were asymmetric, in which leaf traits were more stable than stem traits. Also significant allometric relationships were found among most of the plant functional traits under the four mowing treatments. Sensitive traits of L. chinensis (e.g. leaf length and stem length) were primary indicators associated with aboveground biomass decline under high mowing intensity. In conclusion, the allometric growth of different functional traits of L. chinensis varies with different long-term mowing practices, which is likely to be a strategy used by the plant to adapt to the mowing disturbances.