The bulk phase of nonionic surfactant C10E4 solution was monitored by a dynamic light scattering (DLS) system at 20 degrees C in a narrow range of concentration near the cmc. Two particle aggregations were observed. The DLS data show (i) there exist premicellar multimers (or called submicelles) and (ii) micelles coexist with multimers. The C10E4 sub-micelles have a narrow size distribution with an averaged hydrodynamic diameter (D-h) of 1.35 nm. The D-h of the micelles is around 10.5 nm at 1.0 x 10(-6) mol/mL and increases slightly with C10E4 concentration. It is illustrated from the DLS data that (i) at C = 0.78-0.82 mu mol/mL, monomers and premicellar multimers coexist and (ii) at C = 0.84-0.92 mu mol/mL, monomers + submicellar multimers + micelles coexist. At more elevated concentrations, only the signals from the micelles are detected by DLS. (C) 2007 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.