An object of the present invention is to provide a method of producing acrolein and/or acrylic acid, with which method even when air that contains a lot of floating particles is used as an oxygen source, without suffering from deterioration of catalyst performance owing to coking and so on of the catalyst and inconveniences such as an increase in the pressure difference and clogging of a reaction tube, with a high yield and stably over a long time, acrolein and/or acrylic acid can be produced. The present invention relates to a method of producing acrolein and/or acrylic acid by subjecting propylene or propane to a gas phase oxidation with an oxygen-containing gas under the presence of an oxidation catalyst, wherein as an oxygen source air from which the floating particles are removed is used.