Abstract : This project focused on the mechanisms of soot oxidation by O2. A two-stage burner was used. Soot was generated for ethylene, JP-8 surrogate (n-dodecane/m-xylene), m-xylene, and n-dodecane air premixed flames. Downstream, the soot-laden gases were passed through a secondary flat-flame burner where soot was burned out under fuel-lean or -rich conditions. The process was followed by the evolution of particle size distribution, flame temperature, gas-phase composition, soot morphology and nanostructure. Measurements of soot size distribution and number concentration as a function of the HAB showed particle fragmentation, evidenced by the decrease in particle mean diameter and a significant increase in number concentration in the region where O2 concentration decreased. Higher in the burner, soot was burned as a result of the increase in OH* concentration which produced higher soot oxidation rates. Experimental information from PSDs, temperature, gas-phase composition was used to develop an oxidation kinetic expression that accounts for the effects of temperature, O2, and OH* on the rate of oxidation.