The theological characteristics of the solutions of the whole extracts and their fractions from the Pinus radiata bark were investigated. The viscosity changes upon addition of aqueous NaOH solution into the solutions of the hot water extracts are due mainly to the dissolution of the phlobaphene fraction. The polyelectrolyte character was established from the solutions of the hot-water extracts. The kinetics of the size growth of naturally forming phlobaphenes could be observed by photon correlation spectroscopy (PCS) from the solutions of hot-water extracts. Mild sonication could degrade phlobaphenes partly and this indicates that the formation of phlobaphenes is partly associated with colloidal interaction.