The migration regimes and the separation selectivity of linear poly(styrenesulfonates) (PSS) were investigated in solutions of linear polymeric hydroxyethylcellulose (HEC). Variable parameters were the number of PSS monomer units (in the range of 25-6520), HEC concentration (below and above the entanglement threshold), molecular mass of HEC (between 35900 and 438000 Da) and electric field strength (from 190 to 1140 V/cm). Besides those regimes which are known for migration of polyelectrolytes in physical networks (Ogston sieving, reptation without and with orientation), the observed separation below the entanglement threshold indicates an effect of solute-chain interactions similar to that observed for the separation of double-stranded DNA. From the dependence of the separation selectivity on HEC concentration and molecular weight it was found that both parameters increase the separation. The selectivity of the solutions of higher concentrated low molecular HEC was compared to lower concentrated high molecular HEC, which has a similar bulk viscosity, and therefore obeys comparable peak dispersion due to thermal broadening. At high field strengths (preferably used in capillary electrophoresis) the former gave better separation only for shorter PSS molecules. For separation of longer PSS molecules, only high molecular HEC is applicable due to the deformation of the low molecular matrix by large analyte molecules.