A mathematical model for the quantitative analysis of kinetic data obtained in the hydrolysis of cellulose ethers is described. The model is applied to solution viscosity measurements obtained during the enzymatic hydrolysis of O-(2-hydroxyethyl)cellulose (HEC). Data analysis involves the derivation of the intrinsic viscosity dependence on the enzymatic hydrolysis time, from the analytical expressions of the Martin equation. The scope of the method and its relationship to the resistance to enzymatic degradation of cellulose derivatives are discussed. The importance of the substitution pattern (represented by the degree of substitution) and molecular size (end-to-end distance derived from the Flory-Fox equation), on the biodegradability of HEC is demonstrated.