In the present work urea-formaldehyde resins (UF) containing different amounts of SiO2 nanoparticles were synthesized and studied in depth. All the hybrids were characterized with Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffractometry (XRD), while the dispersion of nanoparticles was studied with scanning electron microscopy with associated energy dispersive X-ray spectrometer (SEM/EDS). It was found that even though silanol groups of SiO2 can interact with UF resin and form hydrogen bonds, aggregates of SiO2 nanoparticles can still be formed in UF resin. Their size increases as SiO2 content is increased. The curing reactions were examined with differential scanning calorimetry (DSC) and it was revealed that curing temperature of OF resin is slightly affected by the addition of nanoparticles. Furthermore, the activation energy of the curing reactions, for every hybrid, was calculated using the Kissinger's method, which implied the existence of interactions between the nanoparticles and the polymer chain. Thermogravimetric analysis (TGA) revealed that SiO2 nanoparticles do not have an effect in the thermal stability of the resin. From the application of the prepared UF/SiO2 resins in wood panels it was found that the mechanical properties of the panels, like the internal bond and the modulus of rapture, are enhanced with increasing nanoSiO(2) concentration. (C) 2011 Elsevier B.V. All rights reserved.