The emergence of engineered nano-materials (ENMs) in the global marketplace and their accidental introduction into the subsurface pose a potential risk to the environment and public health. There is a need for the development of techniques to detect their presence and transport in the subsurface. Complex conductivity measurements have been shown to be sensitive to the presence of metals. Laboratory experiments were conducted to investigate the complex conductivity response of silver (Ag) nanoparticles in a sand column under different nanoparticle concentrations (0, 2, 4, 6, 8 and 10 mg/g) and moisture content (5%, 10%, 15%, 20% and 30%). Complex conductivity measurements were obtained between 0.1-1000 Hz. The results showed that at different water saturation the magnitude of the imaginary conductivity component increased by one order with increasing concentration of Ag nanoparticles with minimal changes in the real conductivity component. On the other hand, at different concentrations of Ag nanoparticles the magnitude of the imaginary conductivity and real conductivity components increased by one and a half order and one order of magnitude, respectively. Our results demonstrate that complex conductivity measurements are sensitive to the presence of nanoparticles in unsaturated porous media which potentially could be used in guiding the detection and remediation processes of such contaminants within the vadose zone.