AbstractFor light scattering analysis of an extremely high molecular weight polymer with large size in solution, use of mixtures of a given polymer with its low molecular weight homologue is described to have great advantages. With such bimodal mixtures as test samples, one can alter the unknown form of the angular variations of scattered lights to a form to be expected and widen the range of the linearity with sin2(ø/2), where ø is the scattering angle. According to the considerations, a sample of linear polystyrene was successfully analysed on a commercial apparatus, Fica 50 to have the weight‐average molecular weight of 27 mill