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We show experimentally and numerically that cholesteric-type metal-dielectric structures, made of twisted sub-wavelength hole elliptical–shaped arrays, exhibit strong optical activity and circular dichroism. The experimental demonstration is carried out with terahertz time-domain spectroscopy measurements on a three layered structure operating around 0.5 THz, leading to a rotary power as high as 1000°/wavelength. The contribution of the chirality factor (κ), permittivity (ɛ), and permeability (μ) is discussed after the retrieval of effective parameters from the complex scattering ones.