Land-use change can alter carbon dynamics and soil organic matter fractions, especially in deeper soil layers, with variations depending on the biome. This study aimed to evaluate the influence of different land-use systems on carbon stocks and soil organic matter fractions in the Caatinga and Cerrado biomes, located in the state of Piaui, Brazil. The study was conducted in areas under three land-use types (native vegetation, pasture, and agriculture), with soil sampling at seven depths (0-10, 10-20, 20-30, 30-40, 40-60, 60-80, and 80-100 cm), totaling 126 sampling units. The following parameters were analyzed: soil organic matter (SOM), total organic carbon (TOC), carbon stock (CSTOCK), particulate organic matter (POM), particulate organic carbon (C-POM), and mineral-associated organic carbon (MOC). Results showed that POM content was significantly higher in the surface layers, with greater accumulation in pasture areas of the Cerrado biome. Carbon stocks in pasture and the agricultural regions did not differ from those in native vegetation in both biomes, indicating low levels of degradation. However, the biomes responded differently to agrarian use, highlighting the need for biome-specific management strategies to maintain soil carbon stocks and ensure soil quality.