Abstract: The experimental measurements of the shear strength of unsaturated soils are uncommonly emloyed in the practical engineering because the unsaturated experimental measurements are time-consuming and costly. Instead, the shear strength of unsaturated soils is commonly estimated from the soil-water characteristic curve (SWCC). In this study, an improved capillary model and a new mathematical equation are proposed for the estimation of the shear strength of unsaturated soils from the SWCC. The proposed equation is verified by the experimental data from the published literatures. It is observed that the soil specimen prepared for the SWCC tests may not be in the same stress state as that prepared for the shearing tests. In other words, the measured SWCC from the conventional Tempe cell and pressure plate may not agree with that of the specimen in the shearing tests. As a result, errors may be introduced in the estimated results of the shear strength of unsaturated soils. Consequently, the SWCCs obtained from the conventional method should be corrected for the estimation of the shear strength of the unsaturated soils with a high confining pressure.