Soil texture and structure have substantial effect on the pore-size distribution index (l). Other factors such as clay mineralogy and sodicity can affect l as well, but have been largely ignored. This research was to predict the changes in total soil porosity from differences in water content, air-entry value (y_a), and l. Six soil samples with differences in soil mineralogy (smectite, smectite-vermiculite, and kaolinite) and soil texture were equilibrated with NaCl-CaCl₂ solutions with sodium adsorption ratios (SAR) of 0, 20, and 50. After the equilibration process, the samples were air-dried and repacked in Plexiglas rings. The soil water characteristic curve was measured using the drying curve method. The pore-size distribution index was determined through linear regression from the water characteristic data. Sodicity significantly increased the volumetric water content (q_v) at a given matric potential, water-volume ratio, shrinkage capacity, and y_a in four of the six test soils, with the smectitic sandy loam and kaolinitic loam soils as the two exceptions. The SAR increase did not affect the water content of the kaolinitic soil. At saturation, when SAR increased from 0 to 50, q_v increased 11% in the smectitic silty-clay loam soil and 10% in the vermiculitic clay loam soil. At –1.5 MPa, q_v increased 64 and 68%, respectively, in the same soils. In the soils with similar clay content, at SAR 50, the shrinkage capacity of the smectitic soils was higher than that of the vermiculitic soil. When clay content and SAR increase, l decreases. When SAR increased from 0 to 50, l decreased 56% in the smectitic silty-clay loam soil and 29% in the smectitic silty-clay soil. The increase in y_a and reduction of l indicates the reduction in the number of larger pores due to sodicity, which causes increased water retention at the same matric potential.