A polymeric capsule shell of high quality is prepared from an aqueous composition which comprises (A) at least one esterified cellulose ether comprising aliphatic monovalent acyl groups and groups of the formula —C(O)—R—COOH, R being a divalent aliphatic or aromatic hydrocarbon group, wherein at least a part of the groups —C(O)—R—COOH are neutralized with an ammonium salt of carbonic acid, formic acid or acetic acid, and (B) from 0 to 7 weight percent of a non-polymeric plasticizer, based on the weight of the esterified cellulose ether, wherein the weight of said at least one esterified cellulose ether is at least 80 percent of the total polymer weight in the aqueous composition.