The intrinsic viscosity [η] of cellulose acetate (CA) has been determined in two solvents: acetic acid (AA) and N,N-dimethylacetamide (DMAC). The samples of this cellulose derivative have a rather weak mean molecular weight MW, with a mean degree of polymerization DP ranging from 213 to 47 and the same origin. We use the theory of Yamakawa for a worm-like chain to obtain the hydrodynamic diameter D and the persistence length q for these samples of CA, and the Mark-Houwink equation to estimate the parameters K and α. These results were compared with the same parameters obtained with previous experimental published results for CA with a high MW. The measurements were also carried out at different temperatures; the intrinsic-viscosity temperature dependence is discussed. The D and q values calculated for the low-MW range allow estimation of the critical concentrations C* for the solutions, which are compared with experimental results.