A process for the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of propene to acrolein, in which the temperature of the fixed catalyst bed is increased over the time and the gas phase partial oxidation is interrupted at least once per calendar year and the gas mixture G consisting of molecular oxygen, inert gas and optionally steam is conducted through the fixed catalyst bed at a temperature of the fixed catalyst bed of from 250 to 550.degree. C.