Crystalline yttrium carbonate, Y2(CO3)3·2.79H2O, was synthesized using ammonium bicarbonate as precipitant. The X ray diffraction data were indexed in the triclinic system with cell parameters a = 19. 076Å, b = 22. 312Å, c = 7. 823Å, α = 94. 493°, β = 91. 397° and γ = 112. 663°. The structure is closely related to those of tengerite type rare earth carbonates in the literature. The IR data for this yttrium carbonate show the presence of two different carbonate groups. The thermal decomposition of yttrium carbonate to oxide occurs via unstable intermediate phases.