Esterified cellulose ethers which comprise (i) aliphatic monovalent acyl groups or (ii) 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, or (iii) a combination of aliphatic monovalent acyl groups and groups of the formula —C(O)—R—COOA, which have a viscosity of up to 2.33 mPa·s, measured as a 2.0 wt % solution of the esterified cellulose ether in 0.43 wt % aqueous NaOH at 20° C., and which have a viscosity of up to 13 mPao·s, measured as a 10 wt % solution of the esterified cellulose ether in acetone at 20° C. are useful for preparing solid dispersions comprising drugs.