The strong optical chirality arising from certain synthetic metamaterials has important and widespread applications in polarization optics,stereochemistry and spintronics.However,these intrinsically chiral metamaterials are restricted to a complicated three-dimensional (3D) geometry,which leads to significant fabrication challenges,particularly at visible wavelengths.Their planar two-dimensional (2D) counterparts are limited by symmetry considerations to operation at oblique angles (extrinsic chirality) and possess significantly weaker chiro-optical responses close to normal incidence.Here,we address the challenge of realizing strong intrinsic chirality from thin,planar dielectric nanostructures.Most notably,we experimentally achieve near-unity circular dichroism with ～ 90％ of the light with the chosen helicity being transmitted at a wavelength of 540 nm.This is the highest value demonstrated to date for any geometry in the visible spectrum.We interpret this result within the charge-current multipole expansion framework and show that the excitation of higher-order multipoles is responsible for the giant circular dichroism.These experimental results enable the realization of high-performance miniaturized chiro-optical components in a scalable manner at optical frequencies.