There is provided a process for producing acrolein, which makes it possible to obtain acrolein in high yield by dehydration of glycerin. Glycerin is allowed to coexist with a catalyst containing a rare earth metal salt crystal of phosphoric acid, thereby dehydrating the glycerin, wherein the crystal is obtained by calcining a solid which is formed by allowing a liquid containing water and a hydroxide of the rare earth metal and/or a dehydration condensate of the hydroxide to contain phosphate ions.