The persistence length and the overlap concentration (c*) of poly(ethylene oxide) (PEO) and hydroxyethylcellulose (HEC) with similar molecular weight in 1 × TBE buffer were studied by laser light scattering and viscometry. Their effect on DNA separation was investigated by capillary electrophoresis. It was determined that the persistence length of HEC was at least 5 times higher than that of PEO. Therefore, the c* of HEC was smaller than that of PEO by a factor of ca. 2.5. It was also found that the c* values determined by laser light scattering were much lower than those by viscometry. We attributed it to the state of polymer chains in which c* was measured: laser light scattering determined the c* in ultradilute solution where the polymer chains were in the static state; while viscometry determined the c* in dilute or semidilute concentration region with polymer chains being in the hydrodynamic flowing state. When used in DNA separation, polymer chains were in different states due to the disturbance of DNA molecules, making c* region dependent. When the real concentration was normalized by c*, PEO and HEC showed almost equal performance in separating ΦX174/Hae III DNA digest in dilute solution, even though their persistence lengths were quite different.