Structure formation during the sol-gel transition of resorcinol-formaldehyde (RF) solutions was traced by dynamic light scattering (DLS) and static light scattering (SLS) techniques. The decay time spectra obtained by DLS revealed that both the growth rates of colloidal particles formed during the early stage of the sol-gel transition and the time required for the colloidal particles to form a firm network structure could be related to the ratio of catalyst to water (C/W) of the starting RF solution. SLS results indicated that the molecular weight of colloidal particles increased with the progress of the sol-gel transition, the rate of which was also affected by the value of C/W. The mesoporosity of RF aerogels, which were prepared by drying RF hydrogels with supercritical carbon dioxide, was confirmed to depend on the size of colloidal particles estimated from the decay time spectrum collected at the last stage of the sol-gel transition. (C) 2002 Elsevier Science.