Grassland management is considered a key factor in the global carbon cycle dynamics. We aimed to evaluate how ecosystem respiration (ER) of grazed systems is influenced by abandonment and determine to which extent abiotic and biotic factors might explain CO2 effluxes. In two subalpine grasslands in the eastern Pyrenees, we established two grazing treatments (abandoned and grazed) randomly distributed in four plots. In each plot, we measured ER using a closed PP-System, EGM-4 CO2 analyzer in four subplots. After each measurement, we recorded soil temperature (T), clipped aboveground biomass and sampled the first 15cm of soil to determine belowground biomass and soil water content (SWC) and to analyze soil organic carbon fractions. In the abandoned plots, CO2 efflux and SWC were significantly higher than in the grazed plots. The main factors explaining CO2 efflux variability were T and SWC. Adding management to this model contributes to a better understanding of ER processes. Results of this work suggest that grassland abandonment increases CO2 efflux from the ecosystem to the atmosphere.