Real-time monitoring of soil water content is of great significance to prevent many engineering accidents, such as landslide, water seepage of foundation dam and reduction of foundation bearing capacity. Smart aggregates (SAs) based on electromechanical impedance (EMI) technique have showed the excellent monitoring capability in various engineering applications, however, there are limited reports on the application in the monitoring of the soil water content. In this paper, the spherical smart aggregates (SSAs) based on the EMI technique were investigated in the monitoring of soil water content. Firstly, the SSAs were designed and fabricated by using the monolithic concrete encapsulation method, and their stable performance in air were evaluated and confirmed by testing and analyzing the impedance spectrum. Then, the fabricated SSAs were immersed into the water environment lasting for 28 days to ensure the stability under working conditions, such as the soil with high water content and the hydration process of early-age concrete. Finally, the monitoring experiments of soil water content were carried out based on the SSAs and the traditional SAs using the EMI method. The measured impedance signatures under different water contents in soil were quantified by three types of statistical indexes, including root mean square deviation (RMSD), mean absolute percentage deviation (MAPD), and correlation coefficient deviation (CCD). The experimental results show that compared to the traditional SAs, the SSAs are more sensitive and stable to monitor the soil water content.