One-dimensional benzene-oxygen-argon (11.5mol% C6H6, 43.2mol% O-2 and 45.3mol% Ar) and benzene- acetylene- oxygen- argon (10.7mol % C6H6, 2.6mol % C2H2, 43.2mol % O-2 and 43.5mol% Ar) flames with an equivalence ratio of 2 were stabilized at low pressure (45 mbar) on a flat flame burner. Gas sampling was achieved by a conical quartz nozzle, at different positions of the flame. Identification and monitoring of chemical species was performed by Molecular Beam Mass Spectrometry (MBMS). Every chemical species was analyzed in both flames, under similar conditions, in order to perform a reliable calibration and a direct comparison. Experimental results and their comparison to simulated data provide interesting clues to evaluate more precisely the role of acetylene in hydrocarbon and PAH production.