A recently developed analytical method of combining off-line laser light scattering (LLS) and size exclusion chromatography (SEC) was used to investigate a set of moderately distributed hydroxyethyl cellulose acetate (HECA) samples in tetrahydrofuran (THF) at room temperature. Our results have shown that this new LLS + SEC method is suitable for the characterization of molecular weight distribution of HECA. By using this method, we have simultaneously determined two calibrations of V (cm(3)) = 45.3 - 1.89 log (M) and D (cm(2)/s) = 2.45 X 10(-4) M(-0.60), where M is the molecular weight of HECA; V, the elution volume in SEC; and D, the translational diffusion coefficient in dynamic LLS. In addition, our results have also indicated that the chain conformation of HECA in THF at room temperature is a slightly extended linear coil.