Light green transparent crystals of Cs₄[UO₂(CO ₃)₃] were prepared by evaporation from aqueous solutions. The crystal structure was refined to R₁ = 0.039 (wR₂ = 0.081) for 2311 reflections with |F_hkl|≥4σ|F_hkl|. Monoclinic system, space group C2/c, a = 11.5131(9), b = 9.6037(8), c = 12.9177(10) Å, β = 93.767(2)°, V = 1425.2(2) ų. The structure of Cs₄[UO₂(CO₃)₃] consists of isolated complex ions [UO₂(CO₃) ₃]^4- formed by uranyl cation UO₂²⁺ and three CO₃^2- groups. The equatorial planes of the [UO₂(CO₃)₃]^4- ions are approximately parallel to the (201) plane. The nine-coordinate Cs⁺ cations are located between the complex anions. The compound is isostructural with M ₄[UO₂(CO₃)₃] with M = K, NH ₄, and Tl, but not isostructural with Na₄[UO ₂(CO₃)₃].