Esterified cellulose ethers which have i) as ester groups aliphatic monovalent acyl groups or a combination of aliphatic monovalent acyl groups and groups of the formula —C(O)—R—COOA wherein R is a divalent aliphatic or aromatic hydrocarbon group and A is hydrogen or a cation, ii) a weight average molecular weight Mw of from 80,000 Dalton to 220,000 Dalton, iii) a Polydispersity Mw/Mn of from 1.3 to 4.0, and iv) an Mz/Mn of not more than 18.5, when the weight average molecular weight Mw, the number average molecular weight Mn and the z-average molecular weight Mz are measured by SEC-MALLS using as mobile phase a mixture produced from 40 parts by volume of acetonitrile and 60 parts by volume of aqueous buffer containing 50 mM NaH2—PO4 and 0.1 M NaNO3. are useful as enteric polymers for pharmaceutical dosage forms.