Langbeinite-type inorganic compounds have a wide range of applications, but nonlinear-optical properties are rarely mentioned in this series. Here, we report a new orthophosphate, LiCs2Y2(PO4)(3), with a langbeinite-type structure, which is the first example in the system of mixed alkali-metal yttrium phosphates. Notably, LiCs2Y2(PO4)(3) exhibits a moderate second-harmonic generation efficiency of 0.9KH(2)PO(4) and is transparent down to 200 nm. In addition, the thermal stability and theory calculations, including the electronic band structure, second-order nonlinear-optical coefficients, and dipole moment analysis, are also reported. This work not only expands the langbeinite-type system but also inspires a study on their nonlinear-optical properties.