The formation process of onion structure in a quaternary mixture made of water, NaCl, octanol and sodium dodecyl sulphate, have been investigated by two dimensional light scattering under various shear rates. In this Letter, we investigated the size evolution of onion structure estimated by light scattering data with a nonlinear least-squares curve fitting method. The time evolution of onion size showed a good agreement with a stretched exponential function. The formation process of onion structure is briefly discussed from the viewpoint of the physical meaning of fitting parameters based on the integral transformation method. (C) 2008 Elsevier B.V. All rights reserved.