A highly charged polyelectrolyte, sodium polystyrenesulfonate, was investigated in various quality of solvent by using dynamic light scattering and viscosity measurements. As the solvent quality was lowered, the relaxation dynamics by the scattering measurements exhibited a drastic change from two relaxations to single one. Furthermore, an obvious reduction of zero‐shear viscosity coincided with the transition. These results indicate that the polyelectrolyte solution system in the solvent region has formed mono‐disperse micelles by strong segregation. The micelle size was estimated to be about 20 nm by Einstein‐Stokes relation. This micelle formation of polyelectrolyte solution system has been achieved experimentally for the first time despite theoretical predicts so far. © 2004 American Institute of Physics