Abstract The objective of this study was to evaluate the use of chemical and physical fractions of soil organic matter ( SOM ), rather than SOM per se , as indicators of soil physical quality ( SPQ ) based on their effect on aggregate stability ( AS ). Chemically extracted humic and fulvic acids ( HA and FA ) were used as chemical fractions, and heavy and light fractions ( HF and LF ) obtained by density separation as physical fractions. The analyses were conducted on medium‐textured soils from tropical and temperate regions under cropland and pasture. Results show that soil organic carbon ( SOC ), SOM fractions and AS appear to be affected by land use regardless of the origin of the soils. A general separation of structurally stable and unstable soils between samples of large and small SOC content, respectively, was observed. SOM fractions did not show a better relationship with AS than SOC per se . In both geographical regions, soils under cropland showed the smallest content of SOC , HA and carbon concentration in LF and HF , and the largest HF / LF ratio (proportion of the HF and LF in percent by mass of bulk soil). With significant associations between AS and SOC content (0.79**), FA / SOC ( r = −0.83* * ), HA / FA ( r = 0.58* * ), carbon concentration of LF ( r = 0.69* * ) and HF ( r = 0.70* * ) and HF / LF ratio ( r = 0.80* * ), cropland showed lowest AS . These associations indicate that SOM fractions provide information about differences in SOM quality in relation to AS and SPQ of soils from tropical and temperate regions under cropland and pasture.