The apparent molecular weight Mw of Na-salts of polyelectrolytesulfonated polysulfone has been determined by small angle laser light scattering in DMF solution which contained NaNO3
LiNO3
LiCl
NaBr and NaI respectively. The results show that the apparent molecular weight of samples in DMF solution contained 0.07 N NaNO3 approach to the true molecular weight Mw.