The influence of the presence of montmorillonite (unmodified and modified) within a resol resin on curing of nanocomposites was studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The acid nature of the clay seems to accelerate primary oxidation processes of resol resin at used temperatures. The nature and amount of clay-modifiers show a strong influence on oxidation reactions and on the rate of curing. In the case of phenylalanine modified montmorillonite (PheMMT), phenylalanine could act in a similar way to formaldehyde due to its reactive groups, leading to an increase of formaldehyde/phenol molar ratio and promoting oxidation at the used temperatures. In the case of a commercial organically modified clay, the presence of long alkyl chains avoids the acceleration of oxidation reactions. The contribution of montmorillonite ions to the oxidation seems to be larger than that of phenylalanine chains. Temperature of curing and state of dispersion of the clay also affect oxidation reactions.