We report measurements of low-frequency dielectric permittivity in two-dimensional θ-(BEDT-TTF)2RbZn(SCN)4 organic compound. The real part of the dielectric permittivity ε' exhibits a sharp peak in the extreme vicinity of the charge ordered phase transition at TCO. The very low magnitude of ε' below TCO results from the lattice dimerization asssociated with the charge ordered phase. We ascribe the temperature-dependent permittivity above TCO to pre-existing charge inhomogeneities—charge disproportionation—as revealed previously by NMR measurements. A qualitative comparison between the dielectric response due to charge order in quasi-one-dimensional conductors and in this two-dimensional system is presented.