The decomposition of plant litter is a fundamental process in the carbon and nutrient cycling of ecosystems, and is an important source of organic and inorganic nutrients for plant growth in grassland ecosystems. It is unclear how environmental factors infl uence the leaf litter decomposition of plants in the Mongolian grasslands. A fi eld experiment was carried out in the meadow steppe of Mungunmorit soum (district), Tuv province, to investigate the eff ects of environmental factors (light-exposed vs. shaded) and leaf traits on leaf litter decomposition of twelve species (Artemisia dracunculus, Aster alpinus, Carex duriuscula, Leontopodium ochroleucum, Leymus chinensis, Poa subfastigata, Potentilla acaulis, Potentilla fruticosa, Potentilla tanacetifolia, Scabiosa comosa, Stellera chamaejasme, and Stipa baicalensis), representing diff erent litter qualities over two years of incubation (6, 12, 18, and 24 months). The research indicated that the leaf litter decomposition signifi cantly varies between species, experimental treatment, and study period; likewise, all their interactions had signifi cant eff ects on weight loss (p < 0.001). Grass species are decomposed relatively slower than the shrubs, herbs, and sedges when comparing the decomposition rates of leaf litters among plant functional groups. The rate of leaf litter decomposition was positively correlated with leaf thickness, specifi c leaf area, and leaf nitrogen and carbon contents, but negatively correlated with leaf dry matter content. In addition, the season has an important eff ect on the decomposition of plant leaves, with the decomposition rate being highest between April and October, while the decomposition rate is very low from November to March. Our research fi ndings suggest that both leaf traits and environmental factors interact to regulate leaf litter decomposition in the Mongolian meadow steppe.