The application of an environmentally friendly modifier-superhydrophobic nano-silicon dioxide (SiO2) on improving the geotechnical characteristics of expansive soil is explored to examine the effect of different percentages of superhydrophobic nano-SiO2 (0.2 %, 0.4 %, 0.6 %, 0.8 %, and 1.0 % by weight of the parent soil) on soil expansion, shrinkage, permeability, and unconfined compressive strength (UCS). Two types of samples, unmodified soil (without nano-SiO2) and modified soil (with nano-SiO2), were used. Results revealed that the shrinkage rate, the Expansion rate, and permeability decreased for the soil samples modified with different contents of superhydrophobic nano-SiO2 and the UCS increased. The shrinkage rate decreased from 3.8 to 2.2 %. The minimum expansion rate of the soil samples modified with superhydrophobic nano-SiO2 was a quarter of that of the unmodified soil. Permeability decreased gradually from 1.38 × 10−8 cm/s to 6.25 × 10−10 cm/s as the superhydrophobic nano-SiO2 content increased. The peak UCS (647 kPa) of modified soil increased by almost 212 % compared with that of the unmodified soil. Superhydrophobic nano-SiO2 helped improve the geotechnical characteristics of expansive soil. In the shrinkage and unconfined compressive tests, 0.6 % nano-SiO2 content had a better effect on the modified soil. In the unloaded expansion and permeability test, the expansion rate and permeability decreased as the nano-SiO2 content increased. After the nano-SiO2 content reached 0.6 %, the decreasing speed became slow. The expansion rate and permeability were similar when the nano-SiO2 contents were 0.6 %, 0.8 %, and 1.0 %, respectively. Therefore, the optimum superhydrophobic nano-SiO2 content was 0.6 %.