An in situ laser light scattering method has been developed for line measurement of aggregate size and morphology. Planar multiangular light scattering measurements were interpreted by using Rayleigh-Debye-Gans scattering theory for fractal aggregates to simultaneously obtain the mean radius of gyration and the fractal dimension along the flame axis, which are the parameters characterizing size and morphology of aggregates. The developed system was applied to study the evolution of silica aggregates produced in a methane/air premixed flat flame. To confirm the suitability of the present method as a line measurement of the growth of aggregates, we compared the results with those obtained by conventional point measurements and it was found that the two results agreed well each other. The comparison of size parameters has been also made with those obtained by thermophoretic sampling and TEM observation. (C) 2003 Elsevier Ltd. All rights reserved.