An esterified cellulose ether of increased weight average molecular weight is produced in a process for reacting a cellulose ether with an aliphatic monocarboxylic acid anhydride and a dicarboxylic acid anhydride, wherein the process comprises the steps of a) preparing a reaction mixture comprising the cellulose ether, the dicarboxylic acid anhydride and a reaction diluent and heating the reaction mixture to a temperature of from 60 C to 110 C prior to, during or after mixing the components of the reaction mixture, and b) adding continuously or in at least three portions the monocarboxylic acid anhydride to the reaction mixture of step a) and completing the reaction.
