Experimental mole fraction profiles of chemical species (stable, radical and intermediates) have been measured in three CH(3)COOH/O(2)/Ar flat premixed flames burning at low pressure (50 mbar) and with equivalence ratios equal to 0.77, 0.9 and 1.05, respectively. The experimental setup used to determine the structure of one-dimensional laminar premixed flames consists of a molecular beam mass spectrometer system (MBMS) combined with electron impact ionisation (El). Experimental results have highlighted an important role played by ketene (CH(2)CO) as an intermediate during the combustion of acetic acid. In order to simulate the experimental results, a sub-mechanism concerning the combustion of CH(3)COOH and CH(2)CO has been built and added to a global mechanism recently proposed. This ensures a reasonably good modelling for the structures of acetic acid flames. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.