The invention relates to a method for preparing acrylic acid from an aqueous glycerol solution, comprising a first step of dehydration of the glycerol to acrolein, carried out in the gas phase in the presence of a catalyst and under a pressure of between 1 and 5 bar, and a second step of oxidation of the acrolein to acrylic acid, in which an intermediate step is implemented, consisting in at least partly condensing the water and heavy by-products present in the stream issuing from the first dehydration step. This method serves to obtain high acrylic acid productivity and selectivity.