The capillary pressure at inter-particle contacts dominates the small-strain behavior of unsaturated soils while the capillarity depends on the particle surface wettability. This study explores the small-strain behavior of both wettable and water-repellent soils using resonant column test. The water-repellency is achieved by coating soils with a hydrophobic agent such as nano-particles. The property of water-repellent soils is classified by optical observation. The microscopic observation using the scanning electron microscope and the atomic force microscopy images confirms the existence of coated nano materials on the silicate mineral surface. The different degrees of saturation and confining pressure are applied to investigate the evolutionary behaviors of small-strain shear stiffness Gmax. The capillary effect is more pronounced at the lower degree of saturation for hydrophilic soils. Results also highlight that synthesized hydrophobic samples have higher stiffness presumably. It is presumably attributed to the surface coating effect by nano-particles to improve the particle interlocking at small strain regime. The hydrophobic agent used in this study not only causes the water repellency but also improve the maximum small-strain stiffness. This observation can be further investigated to engineer natural soils for practical applications.