This study evaluates the effect of an iron precursor incorporation (50 and 1500 ppm by weight) into a commercial diesel and a laboratory-prepared diesel surrogate, not only in the in situ soot reduction capacity, but also in the physicochemical characteristics and reactivity of this carbonaceous material toward oxidation. The in situ soot reduction capacity measurements and the Fe-containing soot sample collection for after-treatment tests were performed in a drop-tube like reactor placed inside of a vertically tubular furnace operated at 900 degrees C. The results indicate that as the iron content in fuel increases, the in situ soot reduction capacity increases up to 50% for commercial diesel and 42% for the diesel surrogate. However, although the soot particles collected on filters did not show significant changes in the main chemical groups due to the fuel additive incorporation, the graphitization degree among samples differs, being structurally more ordered soot particles from pure fuels than those coming from iron-containing fuels. This fact improves the low-temperature reactivity of soot particles after treatment where the apparent activation energy for iron-containing soot samples evaluated in this study was 32% lower than that obtained from soot samples without iron.