<p>It is well recognized that the initial shear modulus is an important parameter for evaluating soil volumetric deformation under shear stress. For unsaturated soils, the initial shear modulus may vary significantly with changes in soil suction. Various mathematical models have been proposed to describe the relationship between the initial shear modulus and soil suction. However, the determination results obtained from these models are highly dependent on model parameters, which are commonly determined through best-fit procedures using experimental data. Consequently, such models have limited predictive capability for estimating the shear modulus of unsaturated soils. In this study, the index properties, soil–water characteristic curves, and measured initial shear modulus values of sandy and silty soils were compiled from published literature. The collected datasets were divided into two groups: one for model development using linear regression analysis and the other for independent verification. During the regression process, the <i>F</i>-test was employed to refine the correlation equations relating model parameters to soil index properties. The proposed correlation equations were subsequently validated using independent datasets for both sandy and silty soils. Based on these results, prediction models are proposed to estimate the initial shear modulus of unsaturated soils directly from soil index properties.</p>