A new compound, K3ZnB5O10, has been synthesized by solid-state reaction. It crystallizes in the monoclinic system, space group P21/n with unit-cell parameters a = 7.6391(5) Å, b = 19.2304(13) Å, c = 7.6905(5) Å, β = 116.698(4)° and Z = 4. The structure of the compound is solved by the direct methods and refined to R1 = 0.0286 and wR2 = 0.0600. K3ZnB5O10 contains a two-dimensional ZnB5O10 layer, which forms by connecting isolated double ring [B5O10] groups and ZnO4 tetrahedra. The K atoms filling in the interlayer and intralayer link the layers together. Functional groups presented in the sample were identified by FTIR spectrum. UV-vis-NIR diffuse reflectance spectrum exhibits ultraviolet cutoff edge is about 190 nm. The DSC analysis proves that K3ZnB5O10 is a congruently melting compound.