The zero-shear viscosity of moderately concentrated solutions of cellulose acetate is studied iJ'l two different solvents namely; cyclohexanone and dioxane to investigate the effect of sol­vent on the polymer viscosity. For each solvent the ratio of the increment in the logarithemic zero­shear viscosity and logarithmic change of concentration (d In "oId InC) is calculated. To find out the effect of both temperature and concentration on the zero- shear viscosity of the polymer, solutions in dioxane are studied at various temperatures and it was concluded that the particle aggregation is af­fected when both the temperature and concentration are changed.