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Conventional grazing, with high grazing pressure imposed during the plant growing season, destroys soil structure and carbon (C) protection mechanisms. Soil C is protected from decomposition by encapsulation in soil aggregates or adsorption with metal oxide mineral fractions. However, the processes by which conventional grazing affects soil C protection and the level of soil organic carbon (SO C) remain unclear. We sampled 15 pairs of sites (180 plots) contrasting grazing exclusion inside the fence and conventional grazing outside the fence, in the temperate steppe of Inner Mongolia, China, to elucidate processes affecting soil C protection and to assess the relative contribution of physical versus mineral protection to SOC. We characterized the physical and mineral protection of C by soil aggregate stability (mean weight diameter, MWD) and soil Fe/Al associated organic C, respectively. Our results showed that conventional grazing decreased SOC content (-14.83%) and weakened SOC physical (-4.88%) and mineral (-10.88%) protection, mainly due to increased soil bulk density and pH, and decreased microbial biomass C, compared with grazing exclusion. I n addition, conventional grazing-induced reductions in plant inputs (root biomass) could indirectly weaken the physical and mineral protection of C. Declined root-derived C inputs will limit microbial biomass C, thus hindering microbial contribution to soi l aggregation and the formation of mineral C fractions. More importantly, we found that destroying physical (57.90%) and mineral (36.76%) protection combined governed the loss of SOC in conventionally grazed grassland. These results imply a need to manage rangelands in a way that retains more litter or root-rich plant species to ensure more plant inputs, promoting physical and mineral protection of soil C.