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Soil organic carbon (SOC) content of grasslands of Chihuahua might vary with range condition. The objective was to estimate SOC on three grassland types under contrasting range conditions in Chihuahua. Soil samples were collected in two different range conditions (poor and good/excellent), two microsites (bare soil and underneath grass), and two soil depths (0-15 and 15-30 cm) in shortgrass prairie, bunchgrass grassland, and halophyte grassland. Soil samples were taken at the beginning and at the end of the growing season in 2010 and at the end of the growing season in 2011. SOC was analyzed with element analyzer at composite samples. Data were analyzed with linear mixed models and repeated measures separately for each grassland type. Carbon stocks were estimated at 0.30 m soil depth and with soil bulk density estimated in each grassland type. Shortgrass prairie SOC varied (P?0.0207) from 0.578±0.03% underneath blue grama (Bouteloua gracilis) to 0.466±0.03% in bare soil. At the bunchgrass grassland, SOC ranged (P?0.0364) from 1.101±0.13% in poor range condition/bare soil to 2.834±0.13% % in excellent range condition/underneath purple muhly (Muhlenbergia rigida). SOC fluctuated (P?0.0036) from 0.315±0.07% at good range condition/15-30cm soil depth to 1.431±0.07% at excellent range condition/0-15cm soil depth in halophyte grassland. Carbon stocks varied from 18 ton ha-1 at the shortgrass prairie, 21 ton ha-1 at the halophyte grassland, and 46 ton ha-1 at the bunchgrass site. SOC varied with grassland type and was mainly affected by range condition and microsite. Bunchgrass grassland, a site with more favorable precipitation, showed the highest carbon stock.