The aim of this paper is to evaluate the effect of the oxygenated compounds concentration on sooting propensities of Diesel and Biodiesel surrogates and to investigate the oxidative reactivity of soot obtained by combustion of these surrogates using an atmospheric axisymmetric co-flow diffusion flame burner. Methyl decanoate (MD) concentrations from 3 to 30 % (in mole %) are added to a Diesel surrogate made up of a binary mixture of 70 % of n-decane and 30 % of α-methylnaphthalene (α-MN). The sooting propensities of these mixtures are estimated through the Yield Sooting Indices (YSIs) in methane diffusion flames doped with 35,000 ppm of surrogate vapors. The characteristics of the soot volume fraction are extracted using the light extinction method (LEM). Additionally, soot generated from the combustion of the model Diesel and Biodiesel fuels were collected, sampled and characterized using physico-chemical techniques. MD addition is found to reduce sooting tendencies. This decrease is more pronounced when the concentration of oxygenate additives 2 increases. On another side, the oxidative reactivity of soot generated from the diffusion flame burner is found to decrease when the Biodiesel percentage increases. Furthermore, soot generated from the combustion of Diesel and Biodiesel surrogates exhibited different behaviors. Biodiesel-derived soot particles were smaller and less reactive than Diesel-derived ones, the latter displaying less ordered graphite-like structures and higher amorphous carbon concentration.