There is provided a process for producing acrolein from glycerin, exhibiting a suppressed decrease in the yield of acrolein with time. In the process for producing acrolein by dehydrating glycerin in the presence of a catalyst containing a metal phosphate, one, or two or more, metal phosphates are used, which are selected from aluminum salts, zirconium salts, manganese salts, alkali metal salts (provided that the alkali metal is sodium, potassium, or cesium, and the ratio between the mole number (M) of the alkali metal and the mole number (P) of phosphoric acid (i.e., M/P ratio) in the metal phosphate is 2.0 or lower), alkali earth metal salts (provided that the ratio between the mole number (M) of the alkali earth metal and the mole number (P) of phosphoric acid (i.e., M/P ratio) in the metal phosphate is 1.0 or lower), and the like.