The present invention relates to a process for synthesizing acrolein, coupling the dehydration of glycerol into acrolein with a reaction for aldol condensation of acetaldehyde, produced in the form of an impurity during the dehydration, by means of formaldehyde.More particularly, the process according to the invention consists in subjecting the gaseous effluent resulting from the glycerol dehydration reaction to cooling, then in first of all carrying out, in a first zone, washing with water and condensation of said gaseous effluent so as to then separate, in a second fractionation zone, firstly, a stream rich in light aldehydes, secondly, a stream rich in water and, thirdly, the acrolein stream, and then in reacting the acetaldehyde contained in the light aldehydes-rich stream resulting from the preceding step with formaldehyde so as to obtain a second acrolein-rich stream by means of an aldol condensation reaction according to the following reaction scheme: CH3—CHO+CH2O→CH2═CH—CHO+H2O and in recycling this second acrolein-rich stream to the preceding step.