The present disclosure relates to a depolarizer based on a metamaterial, which comprises a plurality of sheet layers parallel with each other. Each of the sheet layers has a sheet substrate and a plurality of man-made microstructures attached on the sheet substrate. The sheet substrate is divided into a plurality of identical unit bodies. Each of the unit bodies and one of the man-made microstructures that is attached thereon form a cell that has an anisotropic electromagnetic property. Each of the sheet layers has at least two cells whose optical axes are unparallel with each other. According to the depolarizer based on a metamaterial of the present disclosure, at least two cells whose optical axes are unparallel with each other are disposed in each of the metalmaterial sheet layers. Therefore, when an electromagnetic wave having a uniform polarization property propagates through the metamaterial, at least part of the electromagnetic wave will be changed in polarization property, thus achieving the purpose of depolarization. Moreover, as compared to the prior art, the depolarizer of the present disclosure features a simple structure and is easy to be implemented.