The main objectives of this research consist in achieving both experimental and numerical studies of the combustion of several flames using acetaldehyde as a fuel. Experimental mole fraction profiles of chemical species (stable, radical, and intermediates) have been measured in three CH3CHO/O-2/Ar flat premixed flames stabilized at low pressure (50 mbar) and with equivalence ratios equal to 0.75, 1, and 1.25, 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 ionization (EI). The reaction mechanisms proposed by Yasunaga et al. (2007) and by Marinov (1999) are tested by comparison of model predictions with experimental results. The results show that modeling predicts reactants and products mole fraction profiles reasonably well, but significant differences for many intermediate species remain. In order to improve the predictions for these intermediate species, several improvements on the Marinov's mechanism are suggested. They ensure a reasonably good modeling of the acetaldehyde flame structures.