In this Letter, we propose the design of a non-reciprocal electromagnetic metasurface, which uses a highly nonlinear liquid metamaterial as a source of non-reciprocity. We show that the proposed metasurface, whose thickness is comparable to the wavelength, can exhibit a difference between the transmission coefficients in the forward and backward directions of up to 0.95. Moreover, the particularly high nonlinearity of the liquid metamaterial enables the radiation power required to induce the nonlinear effects to be considerably reduced compared with natural materials. The feasibility of the proposed metasurface has been verified by numerical simulations.