The formation process of onion structure in a quaternary mixture, which consists of water, NaCl, octanol and sodium dodecyl sulfate, has been investigated by two-dimensional light scattering under oscillatory shear flow. In our experiment, we investigate the size evolution of onion structure which is estimated by light scattering data with a nonlinear least-squares curve fitting method. The time evolution of onion size is in good agreement with a stretched exponential function. The effect of oscillatory shear flow on formation process of onions is briefly discussed by considering the physical meaning of fitting parameters based on the integral transformation method. (c) 2009 Elsevier B.V. All rights reserved.