The mineralization of organic carbon in soil is an important process that regulates greenhouse gas emissions, soil organic matter formation, and nutrient availability for soil biota and plants. The decomposition and release of CO₂ from plant residue are important processes that affect soil organic carbon mineralization, and many studies have explored the changes in soil organic carbon following litter addition; however, these studies focus on the effects of single type of litter addition and failed to consider the effects of mixed litter. In both natural and managed ecosystems, plant litter, with different chemical compositions, generally become mixed by the influence of wind, water, or humans, and animals influence the degradation process of organic matter in the soil. Hence, examining the effects of the chemical traits of litter mixtures and litter species diversity on the mineralization of soil organic carbon is of considerable importance. In this study, litters of typical plants Setaria viridis, Phragmites communis Trin, Cleistogenes squarrosa, Lespedeza davurica, and sandy soil from the Horqin dune grassland was collected and incubated in a laboratory for 95 days. In order to explain the effects of mixed-species litter on soil organic carbon mineralization, four single litter species and their mixtures, consisting of all possible 2-, 3-and 4-species combinations, were added to soil in jars. We described the dynamics of organic carbon mineralization rates and calculated the cumulative release of CO₂ for all treatments and the difference between measured and predicted effects for the litter mixture. We also explored the effects of chemical traits and species diversity on soil organic carbon mineralization. The results showed that soil organic carbon mineralization was not influenced by the richness of the litter mixture but was closely related to the litter chemical properties, such as N, C/N, lignin/N, and LOMⅠcontents. This suggests that compared with litter mixture with few species, mixed litter with higher species diversity might have functional redundancy. In most instances, species mixing produced no-additive effect on soil organic carbon mineralization, and synergistic non-additive effects were more common than antagonistic non-additive effects, with 7 vs. 2. When the Lespedeza davurica litter was mixed with the gramineous plant litter, soil organic carbon mineralization showed synergistic effects. When the gramineous plant litter was mixed, soil organic carbon mineralization was antagonistic. This might be in part attributed to the similarity of litter chemical composition between the two litter types or from the spatial heterogeneity of the leaf litter.