We present the first experimental observation of Anderson localization in the terahertz frequency range using plasmonic structures.To accomplish this goal,we designed THz waveguides consisting of a one-dimensional array of rectangular apertures that were fabricated in a freestanding metal foil.Disorder is introduced into the waveguide by offsetting the position of each aperture by a random distance within a prescribed range.For example,for a waveguide with apertures spaced by 250 μm in a periodic waveguide,10％ disorder would correspond to the apertures being shifted by a random value between ± 25 μm along the waveguide axis.We find that for disorder levels below 25％,there is only an increase in the propagation loss along the device.However,for two specific waveguides with 25％ disorder,we observe a spatially localized mode that lies just within the stop band of the device and exhibits a double-sided exponential spatial decay away from the maximum.