A process for preparing acrylic acid from methanol and acetic acid, in which, in a reaction zone A, the methanol is partially oxidized to formaldehyde in a heterogeneously catalyzed gas phase reaction, the product gas mixture A obtained and an acetic acid source are used to obtain a reaction gas input mixture B which comprises acetic acid and formaldehyde and has the acetic acid in excess over the formaldehyde, and the formaldehyde present in reaction gas input mixture B is aldol-condensed to acrylic acid under heterogeneous catalysis in a reaction zone B with acetic acid present in reaction gas input mixture B, and unconverted acetic acid still present alongside the acrylic acid target product in the product gas mixture B obtained is removed therefrom, and the acetic acid removed is recycled into the production of reaction gas input mixture B.