Soil structure is a key factor in soil functioning, its ability to support plant and animal life, and to moderate environmental quality. Soil structure influences soil water/solute movement, soil erosion, crusting, nutrient recycling, ground water pollution and CO 2 emission. Aggregate stability is used as an indicator of soil structure. Aggregation results from the rearrangement, flocculation and cementation of primary soil particles. The objectives of this study were to examine the spatial variability of topsoil aggregate stability and the affecting factors in Isfahan Province. Based on the geology map, 252 soil samples were collected from 0–20 cm depth on a 20 × 20 km network. Stability of large aggregates was measured using the wet sieving method and mean weight diameter (MWD), geometric mean diameter (GMD) and percent of water stable aggregates (WSA) were calculated. Stability of small aggregates was assessed using readily-dispersible clay (RDC). Some soil physical and chemical properties including texture, organic matter, carbonates, gypsum, pH, EC, SAR and CEC were also determined. The impacts of different properties on aggregate stability were evaluated using correlation, stepwise regression and spatial variability analyses. Semi-variogram and kriging techniques were used to analyze the spatial variability of the soil structure indices. Results showed that short-time wet sieving (i.e. 2 min) was suitable for evaluation of aggregate stability of the surface soils in Isfahan Province. The MWD, GMD and WSA were positively and significantly interrelated while they had negative and significant (but weaker) correlations with RDC. The highest correlations belonged to GMD indicating that aggregate-size distribution was predominantly log-normal in the studied soils. The correlation analysis showed that organic matter had least influence on aggregate formation and stability due to low organic matter content in the studied soils. However, clay and gypsum contents have significant influence on aggregate stability, whereas EC, SAR and silt content are among the factors negatively affecting aggregates. While sedimentary parent materials mainly produce stable aggregates due to greater clay and calcium enrichment, coarse-textured metamorphic parent materials result in weaker aggregates. Kriging maps of the soil structure indices have good reliability, although with a low accuracy. Spatial variability analyses indicated that structure of the surface soil was weak and severely degraded in the eastern parts of the Province. In the west and southwest regions, soil aggregate stability is moderately well. Highest correlation coefficients were obtained for RDC suggesting that readily-dispersible clay can suitably evaluate soil structural stability in Isfahan Province. Overall, the results showed weak structural stability of the studied soils. Therefore, it is suggested to preserve and/or increase the soil surface cover (plant cover and gravel pavement) against degrading factors in Isfahan Province.