Monoclinic La1-xCexOHSO4 compounds (0 less than or equal tox less than or equal to1) were hydrothermally synthesized from mixed rare earth nitrates and thiourea at moderate temperature. The crystals grown are all flake-like in morphology and display room temperature ultraviolet luminescence. The mean dimension of the crystals turns smaller, and the luminescent intensity turns stronger following the increase of cerium content in the phosphor compounds.